Empirical ground-motion relations using moderate earthquakes recorded by Medellín–Aburrá Valley (Colombia) strong-motion networks (original) (raw)
Related papers
Pure and Applied Geophysics, 2009
Predictive relations are developed for peak ground acceleration (PGA) from the engineering seismoscope (SRR) records of the 2001 M w 7.7 Bhuj earthquake and 239 strong-motion records of 32 significant aftershocks of 3.1 B M w B 5.6 at epicentral distances of 1 B R B 288 km. We have taken advantage of the recent increase in strong-motion data at close distances to derive new attenuation relation for peak horizontal acceleration in the Kachchh seismic zone, Gujarat. This new analysis uses the Joyner-Boore's method for a magnitude-independent shape, based on geometrical spreading and anelastic attenuation, for the attenuation curve. The resulting attenuation equation is, lnðYÞ ¼ À7:9527 þ 1:4043 M W À ln r 2 jb þ 19:82 2 1=2 À0:0682 S for 3:1 \ M W 7:7 std: dev: r ð Þ : AE0:8243; where, Y is peak horizontal acceleration in g, M w is moment magnitude, r jb is the closest distance to the surface projection of the fault rupture in kilometers, and S is a variable taking the values of 0 and 1 according to the local site geology. S is 0 for a rock site, and, S is 1 for a soil site. The relation differs from previous work in the improved reliability of input parameters and large numbers of strong-motion PGA data recorded at short distances (0-50 km) from the source. The relation is in demonstrable agreement with the recorded strongground motion data from earthquakes of M w 3.5, 4.1, 4.5, 5.6, and 7.7. There are insufficient data from the Kachchh region to adequately judge the relation for the magnitude range 5.7 B M w B 7.7. But, our groundmotion prediction model shows a reasonable correlation with the PGA data of the 29 March, 1999 Chamoli main shock (M w 6.5), validating our ground-motion attenuation model for an M w 6.5 event. However, our groundmotion prediction shows no correlation with the PGA data of the 10 December, 1967 Koyna main shock (M w 6.3). Our ground-motion predictions show more scatter in estimated residual for the distance range (0-30 km), which could be due to the amplification/noise at near stations situated in the Kachchh sedimentary basin. We also noticed smaller residuals for the distance range (30-300 km), which could be due to less amplification/noise at sites distant from the Kachchh basin. However, the observed less residuals for the longer distance range (100-300 km) are less reliable due to the lack of available PGA values in the same distance range.
Earthquake dynamics and the prediction of strong ground motion
2006
A large number of earthquakes have been modelled in detail using seismological, geological and geodetic information. Several common traits have been found for earthquakes kinematics at periods longer than 3s. At these frequencies, all large earthquakes (M>7) appear complex with highly variable slip, and propagate with rupture velocities close to about 80 % of the shear wave speed. Starting from these kinematic inversions, it is possible to use numerical wave propagation models in order to estimate the complete radiated field including near and far field effects. Radiation can be separated into two main components: a near field term responsible for the socalled fling steps due to permanent, geodetic offsets; and the far field that produces pulse like motions. Using seismological scaling relations it is possible to explain the main features of displacement spectra using classical seismological models at long periods. Seismic simulations may now be extended to the frequencies up to a few Hz by means of dynamic rupture propagation, where rupture is simulated starting from the kinematic models. In this talk I will review the main results obtained so far and the new avenues of research that have been opened thanks to new near field earthquake data and the ability to simulate increasingly complex and realistic seismic ruptures in a computer.
The Influence of Magnitude Range on Empirical Ground-Motion Prediction
Bulletin of The Seismological Society of America, 2007
A key issue in the assessment of seismic hazard in regions of lowto-moderate seismicity is the extent to which accelerograms obtained from smallmagnitude earthquakes can be used as the basis for predicting ground motions due to the larger-magnitude events considered in seismic hazard analysis. In essence, the question is whether empirical ground-motion prediction equations can be applied outside their strict range of applicability as defined by the magnitude and distance ranges covered by the datasets from which they are derived. This question is explored by deriving new spectral prediction equations using an extended strong-motion dataset from Europe and the Middle East covering the magnitude range M w 3.0-7.6 and comparing the predictions with previous equations derived using data from only M w 5.0 and above events. The comparisons show that despite their complex functional form, including quadratic magnitude-dependence and magnitude-dependent attenuation, the equations derived from larger-magnitude events should not be extrapolated to predict ground motions from earthquakes of small magnitude. Moreover, the results suggest not only that ground-motion prediction equations cannot be used outside the ranges of their underlying datasets but also that their applicability at the limits of these ranges may be questionable. Although only tested for smaller magnitudes, the results could be interpreted to suggest that predictive equations also cannot be reliably extrapolated to higher magnitudes than those represented in the dataset from which they are derived, a finding that has important implications for seismic hazard analysis.
1976
An empirical model for scaling Fourier Amplitude Spectra of strong earthquake ground acceleration in terms of magnitude, M, epicentral distance, R, and recording site conditions has been presented. The analysis based on this model implies that: (a) the Fourier amplitude spectra of strong-motion accelerations are characterized by greater energy content and relatively larger amplitudes for long-period waves corresponding to larger magnitudes M, (b) the shape of Fourier amplitude spectra does not vary appreciably for the distance range between about 10 and 100 km, and (c) long-period spectral amplitudes (T > 1 sec) recorded on alluvium are on the average 2.5 times greater than amplitudes recorded on basement rocks, whereas short-period (T < 0.2 sec) spectral amplitudes tend to be larger on basement rocks. It has been shown that the uncertainties which are associated with the forecasting of Fourier amplitude spectra in terms of magnitude, epicentral distance, site conditions, and component direction are considerable and lead to the rhnge of spectral amplitudes which for an 80 per cent confidence interval exceed one order of magnitude. A model has been presented which empirically approximates the distribution of Fourier spectrum amplitudes and enables one to estimate the spectral shapes which are not exceeded by the presently available data more than 100 (1-p) per cent of time where p represents the desired confidence level (0 < p <1). No. of Accelerograms Earthquake Used in No.* this Study Magnitude Caltech Report No.
2016
A megathrust subduction earthquake (M w 7.8) struck the coast of Ecuador on 16 April 2016 at 23:58 UTC. This earthquake is one of the best-recorded megathrust events to date. Besides the mainshock, two large aftershocks have been recorded on 18 May 2016 at 7:57 (M w 6.7) and 16:46 (M w 6.9). These data make a significant contribution for understanding the attenuation of ground motions in Ecuador. Peak ground accelerations and spectral accelerations are compared with four ground-motion prediction equations (GMPEs) developed for interface earthquakes, the global Abrahamson et al. (2016) model, the Japanese equations by Zhao, Zhang, et al. (2006) and Ghofrani and Atkinson (2014), and one Chilean equation (Montalva et al., 2017). The four tested GMPEs are providing rather close predictions for the mainshock at distances up to 200 km. However, our results show that high-frequency attenuation is greater for back-arc sites, thus Zhao, Zhang, et al. (2006) and Montalva et al. (2017), who are not taking into account this difference, are not considered further. Residual analyses show that Ghofrani and Atkinson (2014) and Abrahamson et al. (2016) are well predicting the attenuation of ground motions for the mainshock. Comparisons of aftershock observations with the predictions from Abrahamson et al. (2016) indicate that the GMPE provide reasonable fit to the attenuation rates observed. The event terms of the M w 6.7 and 6.9 events are positive but within the expected scatter from worldwide similar earthquakes. The intraevent standard deviations are higher than the intraevent variability of the model, which is partly related to the poorly constrained V S30 proxies. The Pedernales earthquake produced a large sequence of aftershocks, with at least nine events with magnitude higher or equal to 6.0. Important cities are located at short distances (20-30 km), and magnitudes down to 6.0 must be included in seismic-hazard studies. The next step will be to constitute a strong-motion interface database and test the GMPEs with more quantitative methods. Electronic Supplement: Figures of V S30 values based on topography versus rupture distance and difference between reference V S30 and V S30 based on topography versus distance, residuals, event terms, and intraevent standard deviations.
Bulletin of Earthquake Engineering, 2012
We analysed the within-earthquake correlation of ground motion using the strong-motion records accumulated by the TSMIP (Taiwan Strong Motion Instrumentation Program) network in Taiwan during 1993-2009. Two ground-motion prediction equations, which were recently developed for peak ground acceleration (PGA) in the region and based on moment and local magnitude and hypocentral distance, were used for the calculation and analysis of ground-motion residuals. We also used the database containing shear-wave velocity data averaged for the top 30 m of the soil column (Vs30) for the TSMIP stations. We showed that the within-earthquake correlation may vary significantly depending on site classes, gross geological features of the area, and magnitude of earthquakes, records of which dominate the analysed dataset. On the one hand, there is a prominent correspondence between the within-earthquake correlation of PGA residuals and spatial correlation of Vs30 values, which was estimated for particular geological structures (e.g., sedimentary filled basins and large plain areas). On the other hand, the high level of ground-motion correlation (or significant non-random component of residuals) may be caused by the joint influence of soft surface soil and thick sediments and by the path or azimuthal effects. The point-source approximation of extended fault and neglected hanging-and foot-wall effects may also result in non-random residuals. The application of empirical correction factors, which consider the magnitude of earthquakes, source-to-site distance and Vs30 value for given stations, allows for the effective reduction in the level of within-earthquake correlation, as well as the within-earthquake standard deviation. The results of the analysis may be used in practical estimates of seismic
Earthquake Spectra, 2016
We develop a model to predict the effects of topography on earthquake ground motions using a database of small- to medium-magnitude earthquakes from California. The proposed model relies on a parameter called relative elevation that quantifies topography using the elevation of a site relative to its surroundings. We also investigate an alternative parameterization of topography called smoothed curvature. We study the bias in the residuals from the Chiou et al. (2010) ground motion model with respect to these parameters and fit a model to remedy those biases. We then compare these models by assessing their goodness of fit to the data. The proposed model for topographic effects is intended as a correction to the Chiou et al. (2010) small- to medium-magnitude earthquake prediction model.
Earthquake Engineering & Structural Dynamics, 1994
The physical bases and empirical equations for modelling the duration of strong earthquake ground motion in terms of the earthquake magnitude , the epicentral distance and the geological and local soil site conditions are investigated. At 12 narrow frequency bands, the duration of a function of motion f(t), where f(t) is acceleration , velocity or displacement, is defined as the sum of time intervals during which the integral f' f2(r) dr gains a significant portion of its final value. All the records are band-pass filtered through 12 narrow filters and the duration of strong ground motion is studied separately in these frequency bands. It is shown that the duration of strong motion can be modelled as a sum of the source duration, the prolongation due to propagation effects and the prolongation due to the presence of the sediments and local soils. It is shown how the influence of the magnitude on the duration of strong ground motion becomes progressively stronger, in going from low to moderate frequencies, and that the duration is longer for`soft' than for `hard' propagation paths, at low and at moderate frequencies. At high frequencies, the nature of the broadening of the strong motion portion of the record with increasing distance is different , and is most likely related to the diffraction and scattering of the short waves by the velocity inhomogeneities along the wave path. It is also shown that the geological and local soil conditions should both be included in the model. The duration can be prolonged by 3.5 sec at a site on a deep sedimentary layer at frequencies near 0. 5 Hz, and by as much as 5-6 sec by the presence of soft soil underneath the station , at a frequency of about 1 Hz. An empirical equation for a probabilistic estimate of the discrepancies of the predictions by our models relative to the observed data (distribution function of the residuals) is presented.
Characterization of Earthquake Strong Ground Motion
Pure and Applied Geophysics, 2003
Some underwater landslides are triggered by strong ground motions caused by earthquakes. This paper reviews current concepts and trends in the characterization of strong ground motion. Improved empirical ground motion models have been derived from a strong motion data set that has grown markedly over the past decade. However, these empirical models have a large degree of uncertainty because the magnitude-distance-soil category parameterization of these models often oversimplifies reality. This reflects the fact that other conditions that are known to have an important influence on strong ground motions, such as near-fault rupture directivity effects, crustal waveguide effects, and basin response effects, are not treated as parameters of these simple models. Numerical ground motion models based on seismological theory that include these additional effects have been developed and extensively validated against recorded ground motions, and used to estimate the ground motions of past earthquakes and predict the ground motions of future scenario earthquakes.