Yih-min Wu - Profile on Academia.edu (original) (raw)

Papers by Yih-min Wu

An Integrated Regional and On-site Early Warning Approach: Off-line Application to the Mw 6.3, 2009 Central Italy (L’Aquila) earthquake

AGU Fall Meeting Abstracts, Dec 1, 2009

Most of worldwide developed Earthquake Early Warning Systems (EEWS) are conceived as either ``reg... more Most of worldwide developed Earthquake Early Warning Systems (EEWS) are conceived as either ``regional'' (network-based) or ``on-site'' (stand-alone) systems (Kanamori,2005). A regional EEWS is based on a dense sensor network covering a portion or the entirety of an area that is threatened by earthquakes. The relevant source parameters (event location and magnitude) are estimated from the early portion of recorded

Geophysical Journal International, Sep 28, 2010

Most earthquake early warning systems (EEWS) developed so far are conceived as either 'regional' ... more Most earthquake early warning systems (EEWS) developed so far are conceived as either 'regional' (network-based) or 'on-site' (stand-alone) systems. The recent implementation of nationwide, high dynamic range, dense accelerometer arrays makes now available, potentially in real time, unsaturated waveforms of moderate-to-large magnitude earthquakes recorded at very short epicentral distances (<10-20 km). This would allow for a drastic increase of the early warning lead-time, for example, the time between the alert notification and the arrival time of potentially destructive waves at a given target site. By analysing strong motion data from modern accelerograph networks in Japan, Taiwan and Italy, we propose an integrated regional/on-site early warning method, which can be used in the very first seconds after a moderate-to-large earthquake to map the most probable damaged zones. The method is based on the real-time measurement of the period (τ c) and peak displacement (Pd) parameters at stations located at increasing distances from the earthquake epicentre. The recorded values of early warning parameters are compared to threshold values, which are set for a minimum magnitude 6 and instrumental intensity VII, according to the empirical regression analyses of strong motion data. At each recording site the alert level is assigned based on a decisional table with four alert levels defined upon critical values of the parameters Pd and τ c , which are set according to the error bounds estimated on the derived prediction equations. Given a real time, evolutionary estimation of earthquake location from first P arrivals, the method furnishes an estimation of the extent of potential damage zone as inferred from continuously updated averages of the period parameter and from mapping of the alert levels determined at the near-source accelerometer stations. The off-line application of the method to strong motion records of the Mw 6.3, 2009 Central Italy earthquake shows a very consistent match between the rapidly predicted (within a few seconds from the first recorded P wave) and observed damage zone, the latter being mapped from detailed macroseismic surveys a few days after the event. The proposed approach is suitable for Italy, where, during the last two decades, a dense network of wide dynamic-range accelerometer arrays has been deployed by the Department of Civil Protection (DPC), the Istituto Nazionale di Geofisica e Vulcanologia (INGV) and other regional research agencies.

Geoscience Letters

Building an earthquake early warning (EEW) network requires the installation of seismic instrumen... more Building an earthquake early warning (EEW) network requires the installation of seismic instruments around the seismogenic zone. Using low-cost sensors to build a seismic network for EEW and to generate shakemaps is a cost-effective way in the field of seismology. The National Taiwan University (NTU) network employing 762 P-Alert low-cost sensors based on micro-electro-mechanical systems (MEMS) technology is operational for almost the last 10 years in Taiwan. This instrumentation is capable of recording the strong ground motions of up to ± 2 g and is dense enough to record the near-field ground motion. The NTU system has shown its importance during various earthquakes that caused damage in Taiwan. Although the system is capable of acting as a regional as well as an onsite warning system, it is particularly useful for onsite warning. Using real-time seismic signals, each P-Alert device provided a 2–8 s warning time for the near-source earthquake regions situated in the blind zone of ...

Earth, Planets and Space, 2022

Geodetic evidence for slow slip recurrence changed by stress perturbations was rare, especially f... more Geodetic evidence for slow slip recurrence changed by stress perturbations was rare, especially from afterslip following a nearby large earthquake. The first observed slow slip events in the southernmost Ryukyu subduction had occurred in 2005, 2009, and 2015 following the nearby 2002 March 31 M w 7.1 Hualien offshore earthquake. To investigate whether the M w 7.1 earthquake had influenced the occurrence times of the slow slip, we calculated the coseismic slip distribution and afterslip distribution using the surface displacements from onshore Global Navigation Satellite System observations. The stress perturbation on the slow-slip regions caused by the coseismic slip was quantified using the Coulomb failure criteria. We also examined the aftershock distribution and the evolution with time to clarify the stress perturbations from the afterslip offshore. Our results show that the primary afterslip distribution may have overlapped the 2009 and 2015 slow-slip patch at the downdip of the...

The recurrence intervals of slow slip events may increase gradually after a large earthquake duri... more The recurrence intervals of slow slip events may increase gradually after a large earthquake during the afterslip. Stress perturbations during coseismic and postseismic periods may result in such an increase of intervals. However, the increasing recurrence intervals of slow slip events are rarely observed during an afterslip. The evolution process along with the afterslip remains unclear. We report an observation of slow slip events following the 2002 Mw 7.1 Hualien offshore earthquake afterslip in the southernmost Ryukyu subduction zone. Slow slip events in 2005, 2009, and 2015 are adjacent to the Mw 7.1 earthquake hypocenter. An increasing slow-slip interval of 3.1, 4.2, and 6.2 years has been observed after the earthquake. We calculated coseismic and postseismic slips from the Mw 7.1 earthquake and then estimated the Coulomb stress changes in the slow slip region. The Mw 7.1 earthquake has contributed positive Coulomb stresses to both the 2005 slow-slip region and 2009/2015 repea...

Bulletin of the Seismological Society of America, 1997

This article reports the recent progress on real-time seismic monitoring in Taiwan, particularly ... more This article reports the recent progress on real-time seismic monitoring in Taiwan, particularly the real-time strong-motion monitoring by the Taiwan Central Weather Bureau's telemetered seismic network (CWBSN), which is presently aiming at rapid reporting immediately after a large earthquake occurrence. If rapid reporting can be achieved before the arrival of the strong shaking, earthquake early warning will become possible. CWBSN has achieved the generation of the intensity map, epicenter, and magnitude within 1 min of the occurrence of a large earthquake. Both rapid reporting and early warning are principally applied to large (M ≫ 5) events; the requirement of on-scale waveform recording prompted CWBSN in 1995 to integrate strong-motion sensors (e.g., force-balance accelerometers) into its telemetered seismic monitoring system. Time-domain recursive processing is applied to the multi-channel incoming seismic signals by a group of networked personal computers to generate the i...

Bulletin of the Seismological Society of America, 2020

ABSTRACTDuring an earthquake, site effects can play an important role in triggering landslides. T... more ABSTRACTDuring an earthquake, site effects can play an important role in triggering landslides. To document the seismic response of steep hillslopes, we deployed broadband seismometers across a mountain ridge in Taiwan, in an area with a high earthquake-induced landslide hazard. The ridge has a simple, representative shape, and landslides have previously occurred there. Our seismometer array has recorded continuously during more than 1 yr, with both ambient-noise and regional moderate earthquakes as sources. Processing horizontal and vertical signal components, we show that the ridge has a complex response, which we attribute to the combined effects of the subsurface geology and the topographic geometry. Amplification and directionality of ground motion are observed both high and low on the ridge, giving rise to localized, elevated, earthquake-induced landslide hazard. Our database contains earthquakes with mostly similar locations, making it difficult to determine the effect of ear...

Sensors, 2021

Using low-cost sensors to build a seismic network for earthquake early warning (EEW) and to gener... more Using low-cost sensors to build a seismic network for earthquake early warning (EEW) and to generate shakemaps is a cost-effective way in the field of seismology. National Taiwan University (NTU) network employing 748 P-Alert sensors based on micro-electro-mechanical systems (MEMS) technology is operational for almost the last 10 years. This instrumentation is capable of recording the strong ground motions of up to ± 2g and is dense enough to record the near-field ground motion. It has proven effective in generating EEW warnings and delivering real-time shakemaps to the concerned disaster relief agencies to mitigate the earthquake-affected regions. Before 2020, this instrumentation was used to plot peak ground acceleration (PGA) shakemaps only; however, recently it has been upgraded to generate the peak ground velocity (PGV), Central Weather Bureau (CWB) Intensity scale, and spectral acceleration (Sa) shakemaps at different periods as value-added products. After upgradation, the per...

Journal of Earthquake Engineering, 2020

This study aims to estimate attenuation characteristics of the central Himalayan region of India ... more This study aims to estimate attenuation characteristics of the central Himalayan region of India concerning various strong-motion parameters such as Kappa value (κ) and site effects. We have tried to elaborate on the regional structural heterogeneities and their implications towards the seismic hazard assessment of the study region. A total of 81 earthquakes recorded at 50 stations situated in the central Himalayan region of India are used for the purpose. The particular focus is kept on Kappa value, which shows variability from 0.03 s to 0.095 s, inferring the higher values obtained in plains with deep sediment accumulations proving high-frequency energy dissipation and stiff-soil/rocky sites exhibit comparatively limited attenuation accordingly. To substantiate these results various attenuation parameters such as coda wave quality factor (Q c), intrinsic attenuation parameter (Q i), and scattering attenuation parameter (Q s), have been estimated for two regions in the central seismic gap Himalayan region of India employing the single backscattering model and Wennerberg formulation. The estimated values of Q c , Q i , and Q s are found to be highly dependent on frequency in the frequency range 1.5-24 Hz for both the regions. The average frequency-dependent relationships (Q ¼ Q 0 f η) estimated for both regions are Q c ¼ 158f 1:18 and Q c ¼ 194f 1:2 , respectively. The low value of Q 0 shows that the region is highly heterogeneous while the higher value of η indicates higher seismicity in the area. It is also found that intrinsic attenuation is predominant over the scattering attenuation, envisaging the behavior of the wave attenuation through the absorption within the granitic layer at shallow depths. At lower frequencies, Q c values are found close to Q s values, which is in agreement with the theoretical measurements suggesting the presence of complex crustal heterogeneities beneath the region affecting the propagation of seismic waves experiencing considerable decay of energy through scattering. To confirm the aggregate attenuation on the stations, the site characteristics are also determined for examining the behavior of the amplification as the ground motion is comprised of the combined effect of the source, path, and site. The sites are amplified at a predominant frequency (f peak) in between 1.5 to 10 Hz for the central Himalayan region. The different attenuation and amplification parameters like kappa, Q, and site effects can be utilized for detailed seismic hazard analysis (based on ground motion prediction equations) of the area as this region is of great importance from a socioeconomic point of view.

Seismological Research Letters, 2018

We proposed an effective approach to improve the accuracy of offshore earthquake location in the ... more We proposed an effective approach to improve the accuracy of offshore earthquake location in the earthquake early warning (EEW) system of Taiwan. The EEW system was built upon Geiger's method for earthquake location that requires a set of initial estimates (epicenter, depth, and origin time). Because the initial epicenter highly depends on the locations of inland stations, for far offshore events the final solution falls effortlessly into a local minimum which may far away from the actual position. To solve this problem, an approach for choosing a better initial epicenter was proposed. We added predefined initial epicenters on the offshore area and then implemented several programs running Geiger's method simultaneously. Each of the programs adopted a different predefined initial epicenter. The best earthquake location is given by the most timesaving run, assuming that the solution is converged most efficiently related to the closest distance between the initial and true epicenters. The modified method has been tested with the online EEW system from June 2016 to July 2017 for offshore east Taiwan. A total of 60 earthquakes with magnitudes ranging from 3.3 to 6.0 were detected successfully. The results were compared with the estimations from the original EEW system, showing that our proposed method for offshore earthquakes is able to reduce location error by about 4.9 km on average.

Geophysical Research Letters, 2018

It has been reported that earthquake b-values decrease linearly with the differential stresses in... more It has been reported that earthquake b-values decrease linearly with the differential stresses in the continental crust and subduction zones. Here we report a regression-derived relation between earthquake b-values and crustal stresses using the Anderson fault parameter (Aϕ) in a young orogenic belt of Taiwan. This regression relation is well established by using a large and complete earthquake catalog for Taiwan. The data set consists of b-values and Aϕ values derived from relocated earthquakes and focal mechanisms, respectively. Our results show that b-values decrease linearly with the Aϕ values at crustal depths with a high correlation coefficient of À0.9. Thus, b-values could be used as stress indicators for orogenic belts. However, the state of stress is relatively well correlated with the surface geological setting with respect to earthquake b-values in Taiwan. Temporal variations in the b-value could constitute one of the main reasons for the spatial heterogeneity of b-values. We therefore suggest that b-values could be highly sensitive to temporal stress variations.

Seismological Research Letters, 2018

Two earthquakes, M w 8.1 in 2007 and M w 7.1 in 2010, hit the western province of the Solomon Isl... more Two earthquakes, M w 8.1 in 2007 and M w 7.1 in 2010, hit the western province of the Solomon Islands and caused extensive damage, which motivated us to establish a temporary seismic network around the rupture zones of these earthquakes. With the available continuous seismic data recorded from eight seismic stations, we cross correlate the vertical component of ambient-noise records and calculate Rayleigh-wave group velocity dispersion curves for interstation pairs. A genetic algorithm is adopted to fit the averaged dispersion curve and invert a 1D crustal velocity model, which constitutes two layers (upper and lower crust) and a half-space (uppermost mantle). The resulting thickness values for the upper and lower crust are 6.9 and 13.5 km, respectively. The shear-wave velocities (V S) of the upper crust, lower crust, and uppermost mantle are 2.62, 3.54, and 4:10 km=s with V P =V S ratios of 1.745, 1.749, and 1.766, respectively. The differences between the predicted and observed travel times show that our 1D model (WSOLOCrust) has average 0.85-and 0.16-s improvements in travel-time residuals compared with the global iasp91 and local CRUST 1.0 models, respectively. This layered crustal velocity model for the western Solomon Islands can be further used as a referenced velocity model to locate earthquake and tremor sources as well as to perform 3D seismic tomography in this region. Electronic Supplement: Figures showing the misfit of inversion process and the comparison between observed and synthetics and the location of experiments in previous studies and tables listing information about the seismic network, parameters of the genetic algorithm (GA), information of earthquakes used in this study, and results obtained from different 1D models.

Geophysical Journal International, 2019

SUMMARYIn this paper we test whether or not structural and morphological features inherited from ... more SUMMARYIn this paper we test whether or not structural and morphological features inherited from the Eurasian continental margin are affecting the contemporary stress and strain fields in south-central Taiwan. Principal stress directions (σ1, σ2 and σ3) are estimated from the inversion of clustered earthquake focal mechanisms and the direction of the maximum compressive horizontal stress (SH) is calculated throughout the study area. From these data the most likely fault plane orientations and their kinematics are inferred. The results of the stress inversion are then discussed together with the directions of displacement, compressional strain rate and maximum shear strain rate derived from GPS data. These data show that there is a marked contrast in the direction of SH from north to south across the study area, with the direction of SH remaining roughly subparallel to the relative plate motion vector in the north, whereas in the south it rotates nearly 45° counter-clockwise. The dir...

Bulletin of the Seismological Society of America, 2018

The P-alert seismic network, an on-site low-cost earthquake early warning system (EEWS) located i... more The P-alert seismic network, an on-site low-cost earthquake early warning system (EEWS) located in Taiwan, has proven useful in earthquake events since 2010. This dense network can produce detailed shakemaps and identify the direction of the source rupture in near-real time. Based on real-time acceleration signals and the proposed time-dependent anisotropic attenuation relationship with peak ground acceleration (PGA), ShakingAlarm, a regional early warning system add-on to the original P-alert network, can immediately provide (1) an accurate predicted PGA, before the arrival of the observed PGA, that will give a consistent lead time for hazard assessment and emergency response, (2) a predicted shakemap (PSM) that will converge faster to the final reported shakemap than the regional EEWS, and (3) a shake contour area-based magnitude estimation that is robust, even in the absence of a measured shake contour area such as in the case of an offshore earthquake. Taking the 2016 M w 6.4 Meinong earthquake as an example, the 14th second PSM from Shaking-Alarm converges on the final shakemap better than the regional EEWS from the Central Weather Bureau (CWB) in Taiwan. According to our tests, ShakingAlarm provides a warning using modified Mercalli intensity (MMI) V that is consistent with the results of another on-site EEWS (Strategies and Tools for Real Time Earthquake Risk ReducTion [REAKT]). Further performance tests were conducted with another five M L > 5:5 inland earthquakes from 2013 to 2014. Compared with traditional regional EEWSs, ShakingAlarm can effectively identify possible damage regions and provide valuable early warning information (PSM, predicted PGA, and magnitude) for risk mitigation.

Sensors (Basel, Switzerland), Jan 16, 2017

Following the recent establishment of a high-density seismic network equipped with low-cost micro... more Following the recent establishment of a high-density seismic network equipped with low-cost micro-electro-mechanical system (MEMS) P-wave-alert-device (P-Alert) by the earthquake early warning (EEW) research group at the National Taiwan University, a large quantity of strong-motion records from moderate-magnitude earthquakes (ML > 6) around Taiwan has been accumulated. Using a data preprocessing scheme to recover the dynamic average embedded within the P-Alert data, we adopted an automatic baseline correction approach for the P-Alert accelerograms to determine the coseismic deformation (Cd). Comparisons between the Cd values determined using global positioning system (GPS) data, strong-motion records from the P-Alert network, and data from the Taiwan Strong Motion Instrumentation Program (TSMIP) demonstrates that the near-real-time determination of Cd values (>2 cm), which provide crucial information for seismic hazard mitigation, is possible using records from low-cost MEMS a...

Seismological Research Letters, 2016

On 5 February 2016, a moderate earthquake occurred in southwestern Taiwan with M L 6.4 and a foca... more On 5 February 2016, a moderate earthquake occurred in southwestern Taiwan with M L 6.4 and a focal depth of 16.7 km. This earthquake caused damage to a few buildings and 117 casualties. A low-cost earthquake early warning (EEW) system (P-alert) is in operation for the purpose of EEW and for providing near-real-time shake maps. During this event, a detailed shaking map was generated by the P-alert system within 2 min after the earthquake occurrence, and the high shaking regions strongly correlated with the locations in which the damage and casualties occurred. In the field, individual P-alert devices also serve as onsite EEW systems using P-wave information. The individual P-alert provided a 4-8 s lead time before the arrival of violent shaking in the damaged regions. For regional EEW, both the Central Weather Bureau (CWB, official agency) and the P-alert system responded very well. Currently, regional warnings in Taiwan are only provided to cities at epicentral distances of 50 km or more by the CWB. For cities within a 50-km epicentral distance, the P-alert system could be useful for providing onsite EEW. The performance of the P-alert network during this earthquake proves the efficiency of this real-time, low-cost network in terms of early warning (regional and onsite), near-realtime shake maps, rapid reports, and strong-motion data for research purposes. ▴ Figure 1. The tectonic setup of Taiwan. The star depicts the epicenter of the earthquake event on 5 February 2016. The color version of this figure is available only in the electronic edition.

Journal of Asian Earth Sciences, 2017

In this paper, we study (1) the spatial anomalies and (2) the temporal anomalies of soil gas in n... more In this paper, we study (1) the spatial anomalies and (2) the temporal anomalies of soil gas in northern Taiwan. The spatial anomalies of soil gas are related to tectonic faults, while the temporal anomalies of soil gas are associated with pre-earthquake activities. Detailed soil gas sampling was systematically performed, and the analysis of the collected gas species shows that high helium and nitrogen concentrations appear in samples from specific sites, which coincide with the structural setting of the area studied. This analysis indicates the possibility of using these soil gases to determine fault zones in the studied area. Based on the soil gas data, a station (Tapingti) for automatic soil gas monitoring was constructed on an appropriate site at the fault zone. Some anomalous high radon concentrations at certain times can be identified from the dataset, which was generated by the continuous monitoring of soil gas for over a year. Notably, many of these anomalies were observed several hours to a few days before the earthquakes (M L > 3) that occurred in northern Taiwan. By combining the information of epicenters and fault plane solutions of these earthquakes, we find that the shallow earthquakes (<15 km) were mainly strikeslip and normal-type earthquakes, and concentrated within a distance of 30 km to the monitoring site (Group A). The deep earthquakes (>20 km) were mainly thrust-type earthquakes and distributed in greater distances (>45 km) east of the monitoring site (Group B). Such focal mechanisms of earthquakes suggest an extensional and compressional structural domain in the continental crust for Group A and Group B earthquakes, respectively. It is suggested that the pre-earthquake activities associated with the seismicity of Group B may be transmitted along the major decollement in the region below the Tapingti station, leading to the observed soil gas enhancements.

Terrestrial, Atmospheric and Oceanic Sciences, 2016

The 5 th March 2005 earthquake doublet focal mechanism was determined as strike-slip faulting fro... more The 5 th March 2005 earthquake doublet focal mechanism was determined as strike-slip faulting from Harvard and BATS moment tensor inversion. However, based on first motion polarities, the first shock has a normal focal mechanism (Wu et al. 2008a). This discrepancy has caused a debate over the focal mechanism solution because different focal mechanisms have different tectonic implications. Based on the dislocation determination from Global Position System (GPS) measurements, we find this event includes both tensile and strike-slip components. This finding illustrates the reason for the differences in the determined focal mechanisms using two different types of seismic data and analyzing methods. Field mapping and microstructure examination results indicate that the ductile deformation around the study area was characterized by the evolution from transpression to transtension with a predominant strike-slip component, but present-day active structures may be dominated by normal faulting. Thus, the active tensile slip result determined from dislocation modeling strongly suggests that the back arc extension of the Okinawa trough influences the stress state in this region, and changes the major transtension from strike-slip faulting to normal faulting.

Arabian Journal of Geosciences, 2016

In the present work, ground motion is estimated from future scenario earthquakes at different sit... more In the present work, ground motion is estimated from future scenario earthquakes at different sites in Uttarakhand Himalayas in India using empirical Green's function (EGF) technique. The recorded ground motion from April 4, 2011, M w 5.4 earthquake is taken as a basic element. The ground motion is estimated at 24 sites, where the element earthquake was recorded. It is observed from synthesized time histories that sites located near the epicenter may expect accelerations in excess of 1 g. In the present analysis, Dharchula can expect ground accelerations in excess of 1 g. For M w 7.0, the expected peak values of acceleration (A max) and velocity (V max) on horizontal components at different sites range between 11 and 912 gal and 5 and 52 cm/s, respectively. The corresponding values for the Z component range between 8 and 228 gal, and 3 and 14 cm/s, respectively. Similarly, for M w 7.5, the expected A max and V max on horizontal components at different sites range between 25 and 1281 gal and 25 and 102 cm/s, respectively. The corresponding values for the Z component range between 14 to 474 gal, and 15 to 70 cm/s, respectively. The site amplification functions are estimated using the horizontal-to-vertical spectral ratio procedure. Zone IV (on a scale of II to V according to the seismic zonation map for India) response spectrum for 5 % damping is deficient for M w 7.0, while zone V response spectrum is exceeded at several frequencies for same magnitude. For M w 7.5, zone IV response spectrum is conservative (except at some frequencies), while zone V response spectrum is exceeded at many sites. The estimated PGA values can be incorporated in marking the weak areas in the central Himalaya, thereby assisting the designing and construction of new structures.

Natural Hazards, 2016

In present work, seismic hazard from future earthquake is worked out for Delhi region in terms of... more In present work, seismic hazard from future earthquake is worked out for Delhi region in terms of different strong motion parameters such as peak ground acceleration (PGA), characteristics frequency and spectral acceleration (Sa). The earthquake of March 5, 2012, is taken as key earthquake for synthesis. Stochastic finite modeling technique based on dynamic corner frequency initially is used to produce and match the ground motion histories where 2012 earthquake was recorded. The matching is attained in terms of PGA, response spectra and duration. Once a good match is found, the ground motion is estimated for higher magnitude earthquakes (i.e., Mw 6.0 and Mw 6.5). Our work demonstrates that a Mw 6.0 magnitude earthquake in proximity of Delhi will deliver PGA estimations of 20-209 gal (1 cm/s 2 = 1 gal), the lower values occurring at hard rock sites like NDI (IMD) and DJB. Similarly Mw 6.5 earthquake may produce PGA values ranging between 30 and 323 gal. Finally seismic hazard in Delhi and surrounding regions is estimated from Mw 6.5 magnitude earthquake in terms of PGA, Sa and predominant period. Our computation specifies that at short period, the small structures toward eastern and northwestern part of Delhi city may be affected by the earthquakes. For a case of 0.5 s period, Sa values are distributed uniformly at all the places in Delhi, indicating that the buildings with five floors or so may be in danger from future higher magnitude earthquakes. The Sa maps acquired in this study can be utilized to survey the seismic danger of the region and identify vulnerably susceptible areas in and around Delhi from future higher magnitude earthquake.

An Integrated Regional and On-site Early Warning Approach: Off-line Application to the Mw 6.3, 2009 Central Italy (L’Aquila) earthquake

AGU Fall Meeting Abstracts, Dec 1, 2009

Most of worldwide developed Earthquake Early Warning Systems (EEWS) are conceived as either ``reg... more Most of worldwide developed Earthquake Early Warning Systems (EEWS) are conceived as either ``regional&amp;amp;amp;amp;amp;#39;&amp;amp;amp;amp;amp;#39; (network-based) or ``on-site&amp;amp;amp;amp;amp;#39;&amp;amp;amp;amp;amp;#39; (stand-alone) systems (Kanamori,2005). A regional EEWS is based on a dense sensor network covering a portion or the entirety of an area that is threatened by earthquakes. The relevant source parameters (event location and magnitude) are estimated from the early portion of recorded

Geophysical Journal International, Sep 28, 2010

Most earthquake early warning systems (EEWS) developed so far are conceived as either 'regional' ... more Most earthquake early warning systems (EEWS) developed so far are conceived as either 'regional' (network-based) or 'on-site' (stand-alone) systems. The recent implementation of nationwide, high dynamic range, dense accelerometer arrays makes now available, potentially in real time, unsaturated waveforms of moderate-to-large magnitude earthquakes recorded at very short epicentral distances (<10-20 km). This would allow for a drastic increase of the early warning lead-time, for example, the time between the alert notification and the arrival time of potentially destructive waves at a given target site. By analysing strong motion data from modern accelerograph networks in Japan, Taiwan and Italy, we propose an integrated regional/on-site early warning method, which can be used in the very first seconds after a moderate-to-large earthquake to map the most probable damaged zones. The method is based on the real-time measurement of the period (τ c) and peak displacement (Pd) parameters at stations located at increasing distances from the earthquake epicentre. The recorded values of early warning parameters are compared to threshold values, which are set for a minimum magnitude 6 and instrumental intensity VII, according to the empirical regression analyses of strong motion data. At each recording site the alert level is assigned based on a decisional table with four alert levels defined upon critical values of the parameters Pd and τ c , which are set according to the error bounds estimated on the derived prediction equations. Given a real time, evolutionary estimation of earthquake location from first P arrivals, the method furnishes an estimation of the extent of potential damage zone as inferred from continuously updated averages of the period parameter and from mapping of the alert levels determined at the near-source accelerometer stations. The off-line application of the method to strong motion records of the Mw 6.3, 2009 Central Italy earthquake shows a very consistent match between the rapidly predicted (within a few seconds from the first recorded P wave) and observed damage zone, the latter being mapped from detailed macroseismic surveys a few days after the event. The proposed approach is suitable for Italy, where, during the last two decades, a dense network of wide dynamic-range accelerometer arrays has been deployed by the Department of Civil Protection (DPC), the Istituto Nazionale di Geofisica e Vulcanologia (INGV) and other regional research agencies.

Geoscience Letters

Building an earthquake early warning (EEW) network requires the installation of seismic instrumen... more Building an earthquake early warning (EEW) network requires the installation of seismic instruments around the seismogenic zone. Using low-cost sensors to build a seismic network for EEW and to generate shakemaps is a cost-effective way in the field of seismology. The National Taiwan University (NTU) network employing 762 P-Alert low-cost sensors based on micro-electro-mechanical systems (MEMS) technology is operational for almost the last 10 years in Taiwan. This instrumentation is capable of recording the strong ground motions of up to ± 2 g and is dense enough to record the near-field ground motion. The NTU system has shown its importance during various earthquakes that caused damage in Taiwan. Although the system is capable of acting as a regional as well as an onsite warning system, it is particularly useful for onsite warning. Using real-time seismic signals, each P-Alert device provided a 2–8 s warning time for the near-source earthquake regions situated in the blind zone of ...

Earth, Planets and Space, 2022

Geodetic evidence for slow slip recurrence changed by stress perturbations was rare, especially f... more Geodetic evidence for slow slip recurrence changed by stress perturbations was rare, especially from afterslip following a nearby large earthquake. The first observed slow slip events in the southernmost Ryukyu subduction had occurred in 2005, 2009, and 2015 following the nearby 2002 March 31 M w 7.1 Hualien offshore earthquake. To investigate whether the M w 7.1 earthquake had influenced the occurrence times of the slow slip, we calculated the coseismic slip distribution and afterslip distribution using the surface displacements from onshore Global Navigation Satellite System observations. The stress perturbation on the slow-slip regions caused by the coseismic slip was quantified using the Coulomb failure criteria. We also examined the aftershock distribution and the evolution with time to clarify the stress perturbations from the afterslip offshore. Our results show that the primary afterslip distribution may have overlapped the 2009 and 2015 slow-slip patch at the downdip of the...

The recurrence intervals of slow slip events may increase gradually after a large earthquake duri... more The recurrence intervals of slow slip events may increase gradually after a large earthquake during the afterslip. Stress perturbations during coseismic and postseismic periods may result in such an increase of intervals. However, the increasing recurrence intervals of slow slip events are rarely observed during an afterslip. The evolution process along with the afterslip remains unclear. We report an observation of slow slip events following the 2002 Mw 7.1 Hualien offshore earthquake afterslip in the southernmost Ryukyu subduction zone. Slow slip events in 2005, 2009, and 2015 are adjacent to the Mw 7.1 earthquake hypocenter. An increasing slow-slip interval of 3.1, 4.2, and 6.2 years has been observed after the earthquake. We calculated coseismic and postseismic slips from the Mw 7.1 earthquake and then estimated the Coulomb stress changes in the slow slip region. The Mw 7.1 earthquake has contributed positive Coulomb stresses to both the 2005 slow-slip region and 2009/2015 repea...

Bulletin of the Seismological Society of America, 1997

This article reports the recent progress on real-time seismic monitoring in Taiwan, particularly ... more This article reports the recent progress on real-time seismic monitoring in Taiwan, particularly the real-time strong-motion monitoring by the Taiwan Central Weather Bureau's telemetered seismic network (CWBSN), which is presently aiming at rapid reporting immediately after a large earthquake occurrence. If rapid reporting can be achieved before the arrival of the strong shaking, earthquake early warning will become possible. CWBSN has achieved the generation of the intensity map, epicenter, and magnitude within 1 min of the occurrence of a large earthquake. Both rapid reporting and early warning are principally applied to large (M ≫ 5) events; the requirement of on-scale waveform recording prompted CWBSN in 1995 to integrate strong-motion sensors (e.g., force-balance accelerometers) into its telemetered seismic monitoring system. Time-domain recursive processing is applied to the multi-channel incoming seismic signals by a group of networked personal computers to generate the i...

Bulletin of the Seismological Society of America, 2020

ABSTRACTDuring an earthquake, site effects can play an important role in triggering landslides. T... more ABSTRACTDuring an earthquake, site effects can play an important role in triggering landslides. To document the seismic response of steep hillslopes, we deployed broadband seismometers across a mountain ridge in Taiwan, in an area with a high earthquake-induced landslide hazard. The ridge has a simple, representative shape, and landslides have previously occurred there. Our seismometer array has recorded continuously during more than 1 yr, with both ambient-noise and regional moderate earthquakes as sources. Processing horizontal and vertical signal components, we show that the ridge has a complex response, which we attribute to the combined effects of the subsurface geology and the topographic geometry. Amplification and directionality of ground motion are observed both high and low on the ridge, giving rise to localized, elevated, earthquake-induced landslide hazard. Our database contains earthquakes with mostly similar locations, making it difficult to determine the effect of ear...

Sensors, 2021

Using low-cost sensors to build a seismic network for earthquake early warning (EEW) and to gener... more Using low-cost sensors to build a seismic network for earthquake early warning (EEW) and to generate shakemaps is a cost-effective way in the field of seismology. National Taiwan University (NTU) network employing 748 P-Alert sensors based on micro-electro-mechanical systems (MEMS) technology is operational for almost the last 10 years. This instrumentation is capable of recording the strong ground motions of up to ± 2g and is dense enough to record the near-field ground motion. It has proven effective in generating EEW warnings and delivering real-time shakemaps to the concerned disaster relief agencies to mitigate the earthquake-affected regions. Before 2020, this instrumentation was used to plot peak ground acceleration (PGA) shakemaps only; however, recently it has been upgraded to generate the peak ground velocity (PGV), Central Weather Bureau (CWB) Intensity scale, and spectral acceleration (Sa) shakemaps at different periods as value-added products. After upgradation, the per...

Journal of Earthquake Engineering, 2020

This study aims to estimate attenuation characteristics of the central Himalayan region of India ... more This study aims to estimate attenuation characteristics of the central Himalayan region of India concerning various strong-motion parameters such as Kappa value (κ) and site effects. We have tried to elaborate on the regional structural heterogeneities and their implications towards the seismic hazard assessment of the study region. A total of 81 earthquakes recorded at 50 stations situated in the central Himalayan region of India are used for the purpose. The particular focus is kept on Kappa value, which shows variability from 0.03 s to 0.095 s, inferring the higher values obtained in plains with deep sediment accumulations proving high-frequency energy dissipation and stiff-soil/rocky sites exhibit comparatively limited attenuation accordingly. To substantiate these results various attenuation parameters such as coda wave quality factor (Q c), intrinsic attenuation parameter (Q i), and scattering attenuation parameter (Q s), have been estimated for two regions in the central seismic gap Himalayan region of India employing the single backscattering model and Wennerberg formulation. The estimated values of Q c , Q i , and Q s are found to be highly dependent on frequency in the frequency range 1.5-24 Hz for both the regions. The average frequency-dependent relationships (Q ¼ Q 0 f η) estimated for both regions are Q c ¼ 158f 1:18 and Q c ¼ 194f 1:2 , respectively. The low value of Q 0 shows that the region is highly heterogeneous while the higher value of η indicates higher seismicity in the area. It is also found that intrinsic attenuation is predominant over the scattering attenuation, envisaging the behavior of the wave attenuation through the absorption within the granitic layer at shallow depths. At lower frequencies, Q c values are found close to Q s values, which is in agreement with the theoretical measurements suggesting the presence of complex crustal heterogeneities beneath the region affecting the propagation of seismic waves experiencing considerable decay of energy through scattering. To confirm the aggregate attenuation on the stations, the site characteristics are also determined for examining the behavior of the amplification as the ground motion is comprised of the combined effect of the source, path, and site. The sites are amplified at a predominant frequency (f peak) in between 1.5 to 10 Hz for the central Himalayan region. The different attenuation and amplification parameters like kappa, Q, and site effects can be utilized for detailed seismic hazard analysis (based on ground motion prediction equations) of the area as this region is of great importance from a socioeconomic point of view.

Seismological Research Letters, 2018

We proposed an effective approach to improve the accuracy of offshore earthquake location in the ... more We proposed an effective approach to improve the accuracy of offshore earthquake location in the earthquake early warning (EEW) system of Taiwan. The EEW system was built upon Geiger's method for earthquake location that requires a set of initial estimates (epicenter, depth, and origin time). Because the initial epicenter highly depends on the locations of inland stations, for far offshore events the final solution falls effortlessly into a local minimum which may far away from the actual position. To solve this problem, an approach for choosing a better initial epicenter was proposed. We added predefined initial epicenters on the offshore area and then implemented several programs running Geiger's method simultaneously. Each of the programs adopted a different predefined initial epicenter. The best earthquake location is given by the most timesaving run, assuming that the solution is converged most efficiently related to the closest distance between the initial and true epicenters. The modified method has been tested with the online EEW system from June 2016 to July 2017 for offshore east Taiwan. A total of 60 earthquakes with magnitudes ranging from 3.3 to 6.0 were detected successfully. The results were compared with the estimations from the original EEW system, showing that our proposed method for offshore earthquakes is able to reduce location error by about 4.9 km on average.

Geophysical Research Letters, 2018

It has been reported that earthquake b-values decrease linearly with the differential stresses in... more It has been reported that earthquake b-values decrease linearly with the differential stresses in the continental crust and subduction zones. Here we report a regression-derived relation between earthquake b-values and crustal stresses using the Anderson fault parameter (Aϕ) in a young orogenic belt of Taiwan. This regression relation is well established by using a large and complete earthquake catalog for Taiwan. The data set consists of b-values and Aϕ values derived from relocated earthquakes and focal mechanisms, respectively. Our results show that b-values decrease linearly with the Aϕ values at crustal depths with a high correlation coefficient of À0.9. Thus, b-values could be used as stress indicators for orogenic belts. However, the state of stress is relatively well correlated with the surface geological setting with respect to earthquake b-values in Taiwan. Temporal variations in the b-value could constitute one of the main reasons for the spatial heterogeneity of b-values. We therefore suggest that b-values could be highly sensitive to temporal stress variations.

Seismological Research Letters, 2018

Two earthquakes, M w 8.1 in 2007 and M w 7.1 in 2010, hit the western province of the Solomon Isl... more Two earthquakes, M w 8.1 in 2007 and M w 7.1 in 2010, hit the western province of the Solomon Islands and caused extensive damage, which motivated us to establish a temporary seismic network around the rupture zones of these earthquakes. With the available continuous seismic data recorded from eight seismic stations, we cross correlate the vertical component of ambient-noise records and calculate Rayleigh-wave group velocity dispersion curves for interstation pairs. A genetic algorithm is adopted to fit the averaged dispersion curve and invert a 1D crustal velocity model, which constitutes two layers (upper and lower crust) and a half-space (uppermost mantle). The resulting thickness values for the upper and lower crust are 6.9 and 13.5 km, respectively. The shear-wave velocities (V S) of the upper crust, lower crust, and uppermost mantle are 2.62, 3.54, and 4:10 km=s with V P =V S ratios of 1.745, 1.749, and 1.766, respectively. The differences between the predicted and observed travel times show that our 1D model (WSOLOCrust) has average 0.85-and 0.16-s improvements in travel-time residuals compared with the global iasp91 and local CRUST 1.0 models, respectively. This layered crustal velocity model for the western Solomon Islands can be further used as a referenced velocity model to locate earthquake and tremor sources as well as to perform 3D seismic tomography in this region. Electronic Supplement: Figures showing the misfit of inversion process and the comparison between observed and synthetics and the location of experiments in previous studies and tables listing information about the seismic network, parameters of the genetic algorithm (GA), information of earthquakes used in this study, and results obtained from different 1D models.

Geophysical Journal International, 2019

SUMMARYIn this paper we test whether or not structural and morphological features inherited from ... more SUMMARYIn this paper we test whether or not structural and morphological features inherited from the Eurasian continental margin are affecting the contemporary stress and strain fields in south-central Taiwan. Principal stress directions (σ1, σ2 and σ3) are estimated from the inversion of clustered earthquake focal mechanisms and the direction of the maximum compressive horizontal stress (SH) is calculated throughout the study area. From these data the most likely fault plane orientations and their kinematics are inferred. The results of the stress inversion are then discussed together with the directions of displacement, compressional strain rate and maximum shear strain rate derived from GPS data. These data show that there is a marked contrast in the direction of SH from north to south across the study area, with the direction of SH remaining roughly subparallel to the relative plate motion vector in the north, whereas in the south it rotates nearly 45° counter-clockwise. The dir...

Bulletin of the Seismological Society of America, 2018

The P-alert seismic network, an on-site low-cost earthquake early warning system (EEWS) located i... more The P-alert seismic network, an on-site low-cost earthquake early warning system (EEWS) located in Taiwan, has proven useful in earthquake events since 2010. This dense network can produce detailed shakemaps and identify the direction of the source rupture in near-real time. Based on real-time acceleration signals and the proposed time-dependent anisotropic attenuation relationship with peak ground acceleration (PGA), ShakingAlarm, a regional early warning system add-on to the original P-alert network, can immediately provide (1) an accurate predicted PGA, before the arrival of the observed PGA, that will give a consistent lead time for hazard assessment and emergency response, (2) a predicted shakemap (PSM) that will converge faster to the final reported shakemap than the regional EEWS, and (3) a shake contour area-based magnitude estimation that is robust, even in the absence of a measured shake contour area such as in the case of an offshore earthquake. Taking the 2016 M w 6.4 Meinong earthquake as an example, the 14th second PSM from Shaking-Alarm converges on the final shakemap better than the regional EEWS from the Central Weather Bureau (CWB) in Taiwan. According to our tests, ShakingAlarm provides a warning using modified Mercalli intensity (MMI) V that is consistent with the results of another on-site EEWS (Strategies and Tools for Real Time Earthquake Risk ReducTion [REAKT]). Further performance tests were conducted with another five M L > 5:5 inland earthquakes from 2013 to 2014. Compared with traditional regional EEWSs, ShakingAlarm can effectively identify possible damage regions and provide valuable early warning information (PSM, predicted PGA, and magnitude) for risk mitigation.

Sensors (Basel, Switzerland), Jan 16, 2017

Following the recent establishment of a high-density seismic network equipped with low-cost micro... more Following the recent establishment of a high-density seismic network equipped with low-cost micro-electro-mechanical system (MEMS) P-wave-alert-device (P-Alert) by the earthquake early warning (EEW) research group at the National Taiwan University, a large quantity of strong-motion records from moderate-magnitude earthquakes (ML > 6) around Taiwan has been accumulated. Using a data preprocessing scheme to recover the dynamic average embedded within the P-Alert data, we adopted an automatic baseline correction approach for the P-Alert accelerograms to determine the coseismic deformation (Cd). Comparisons between the Cd values determined using global positioning system (GPS) data, strong-motion records from the P-Alert network, and data from the Taiwan Strong Motion Instrumentation Program (TSMIP) demonstrates that the near-real-time determination of Cd values (>2 cm), which provide crucial information for seismic hazard mitigation, is possible using records from low-cost MEMS a...

Seismological Research Letters, 2016

On 5 February 2016, a moderate earthquake occurred in southwestern Taiwan with M L 6.4 and a foca... more On 5 February 2016, a moderate earthquake occurred in southwestern Taiwan with M L 6.4 and a focal depth of 16.7 km. This earthquake caused damage to a few buildings and 117 casualties. A low-cost earthquake early warning (EEW) system (P-alert) is in operation for the purpose of EEW and for providing near-real-time shake maps. During this event, a detailed shaking map was generated by the P-alert system within 2 min after the earthquake occurrence, and the high shaking regions strongly correlated with the locations in which the damage and casualties occurred. In the field, individual P-alert devices also serve as onsite EEW systems using P-wave information. The individual P-alert provided a 4-8 s lead time before the arrival of violent shaking in the damaged regions. For regional EEW, both the Central Weather Bureau (CWB, official agency) and the P-alert system responded very well. Currently, regional warnings in Taiwan are only provided to cities at epicentral distances of 50 km or more by the CWB. For cities within a 50-km epicentral distance, the P-alert system could be useful for providing onsite EEW. The performance of the P-alert network during this earthquake proves the efficiency of this real-time, low-cost network in terms of early warning (regional and onsite), near-realtime shake maps, rapid reports, and strong-motion data for research purposes. ▴ Figure 1. The tectonic setup of Taiwan. The star depicts the epicenter of the earthquake event on 5 February 2016. The color version of this figure is available only in the electronic edition.

Journal of Asian Earth Sciences, 2017

In this paper, we study (1) the spatial anomalies and (2) the temporal anomalies of soil gas in n... more In this paper, we study (1) the spatial anomalies and (2) the temporal anomalies of soil gas in northern Taiwan. The spatial anomalies of soil gas are related to tectonic faults, while the temporal anomalies of soil gas are associated with pre-earthquake activities. Detailed soil gas sampling was systematically performed, and the analysis of the collected gas species shows that high helium and nitrogen concentrations appear in samples from specific sites, which coincide with the structural setting of the area studied. This analysis indicates the possibility of using these soil gases to determine fault zones in the studied area. Based on the soil gas data, a station (Tapingti) for automatic soil gas monitoring was constructed on an appropriate site at the fault zone. Some anomalous high radon concentrations at certain times can be identified from the dataset, which was generated by the continuous monitoring of soil gas for over a year. Notably, many of these anomalies were observed several hours to a few days before the earthquakes (M L > 3) that occurred in northern Taiwan. By combining the information of epicenters and fault plane solutions of these earthquakes, we find that the shallow earthquakes (<15 km) were mainly strikeslip and normal-type earthquakes, and concentrated within a distance of 30 km to the monitoring site (Group A). The deep earthquakes (>20 km) were mainly thrust-type earthquakes and distributed in greater distances (>45 km) east of the monitoring site (Group B). Such focal mechanisms of earthquakes suggest an extensional and compressional structural domain in the continental crust for Group A and Group B earthquakes, respectively. It is suggested that the pre-earthquake activities associated with the seismicity of Group B may be transmitted along the major decollement in the region below the Tapingti station, leading to the observed soil gas enhancements.

Terrestrial, Atmospheric and Oceanic Sciences, 2016

The 5 th March 2005 earthquake doublet focal mechanism was determined as strike-slip faulting fro... more The 5 th March 2005 earthquake doublet focal mechanism was determined as strike-slip faulting from Harvard and BATS moment tensor inversion. However, based on first motion polarities, the first shock has a normal focal mechanism (Wu et al. 2008a). This discrepancy has caused a debate over the focal mechanism solution because different focal mechanisms have different tectonic implications. Based on the dislocation determination from Global Position System (GPS) measurements, we find this event includes both tensile and strike-slip components. This finding illustrates the reason for the differences in the determined focal mechanisms using two different types of seismic data and analyzing methods. Field mapping and microstructure examination results indicate that the ductile deformation around the study area was characterized by the evolution from transpression to transtension with a predominant strike-slip component, but present-day active structures may be dominated by normal faulting. Thus, the active tensile slip result determined from dislocation modeling strongly suggests that the back arc extension of the Okinawa trough influences the stress state in this region, and changes the major transtension from strike-slip faulting to normal faulting.

Arabian Journal of Geosciences, 2016

In the present work, ground motion is estimated from future scenario earthquakes at different sit... more In the present work, ground motion is estimated from future scenario earthquakes at different sites in Uttarakhand Himalayas in India using empirical Green's function (EGF) technique. The recorded ground motion from April 4, 2011, M w 5.4 earthquake is taken as a basic element. The ground motion is estimated at 24 sites, where the element earthquake was recorded. It is observed from synthesized time histories that sites located near the epicenter may expect accelerations in excess of 1 g. In the present analysis, Dharchula can expect ground accelerations in excess of 1 g. For M w 7.0, the expected peak values of acceleration (A max) and velocity (V max) on horizontal components at different sites range between 11 and 912 gal and 5 and 52 cm/s, respectively. The corresponding values for the Z component range between 8 and 228 gal, and 3 and 14 cm/s, respectively. Similarly, for M w 7.5, the expected A max and V max on horizontal components at different sites range between 25 and 1281 gal and 25 and 102 cm/s, respectively. The corresponding values for the Z component range between 14 to 474 gal, and 15 to 70 cm/s, respectively. The site amplification functions are estimated using the horizontal-to-vertical spectral ratio procedure. Zone IV (on a scale of II to V according to the seismic zonation map for India) response spectrum for 5 % damping is deficient for M w 7.0, while zone V response spectrum is exceeded at several frequencies for same magnitude. For M w 7.5, zone IV response spectrum is conservative (except at some frequencies), while zone V response spectrum is exceeded at many sites. The estimated PGA values can be incorporated in marking the weak areas in the central Himalaya, thereby assisting the designing and construction of new structures.

Natural Hazards, 2016

In present work, seismic hazard from future earthquake is worked out for Delhi region in terms of... more In present work, seismic hazard from future earthquake is worked out for Delhi region in terms of different strong motion parameters such as peak ground acceleration (PGA), characteristics frequency and spectral acceleration (Sa). The earthquake of March 5, 2012, is taken as key earthquake for synthesis. Stochastic finite modeling technique based on dynamic corner frequency initially is used to produce and match the ground motion histories where 2012 earthquake was recorded. The matching is attained in terms of PGA, response spectra and duration. Once a good match is found, the ground motion is estimated for higher magnitude earthquakes (i.e., Mw 6.0 and Mw 6.5). Our work demonstrates that a Mw 6.0 magnitude earthquake in proximity of Delhi will deliver PGA estimations of 20-209 gal (1 cm/s 2 = 1 gal), the lower values occurring at hard rock sites like NDI (IMD) and DJB. Similarly Mw 6.5 earthquake may produce PGA values ranging between 30 and 323 gal. Finally seismic hazard in Delhi and surrounding regions is estimated from Mw 6.5 magnitude earthquake in terms of PGA, Sa and predominant period. Our computation specifies that at short period, the small structures toward eastern and northwestern part of Delhi city may be affected by the earthquakes. For a case of 0.5 s period, Sa values are distributed uniformly at all the places in Delhi, indicating that the buildings with five floors or so may be in danger from future higher magnitude earthquakes. The Sa maps acquired in this study can be utilized to survey the seismic danger of the region and identify vulnerably susceptible areas in and around Delhi from future higher magnitude earthquake.