Revised ML Determination for Crustal Earthquakes in Taiwan (original) (raw)
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Geophysical Journal International Quantifying the seismicity on Taiwan
We quantify the seismicity on the island of Taiwan using the frequency-magnitude statistics of earthquakes since 1900. A break in Gutenberg-Richter scaling for large earthquakes in global seismicity has been observed, this break is also observed in our Taiwan study. The seismic data from the Central Weather Bureau Seismic Network are in good agreement with the Gutenberg-Richter relation taking b ≈ 1 when M < 7. For large earthquakes, M ≥ 7, the seismic data fit Gutenberg-Richter scaling with b ≈ 1.5. If the Gutenberg-Richter scaling for M < 7 earthquakes is extrapolated to larger earthquakes, we would expect a M > 8 earthquake in the study region about every 25 yr. However, our analysis shows a lower frequency of occurrence of large earthquakes so that the expected frequency of M > 8 earthquakes is about 200 yr. The level of seismicity for smaller earthquakes on Taiwan is about 12 times greater than in Southern California and the possibility of a M ≈ 9 earthquake north or south of Taiwan cannot be ruled out. In light of the Fukushima, Japan nuclear disaster, we also discuss the implications of our study for the three operating nuclear power plants on the coast of Taiwan.
Quantifying the seismicity on Taiwan
Geophysical Journal International, 2013
We quantify the seismicity on the island of Taiwan using the frequency-magnitude statistics of earthquakes since 1900. A break in Gutenberg-Richter scaling for large earthquakes in global seismicity has been observed, this break is also observed in our Taiwan study. The seismic data from the Central Weather Bureau Seismic Network are in good agreement with the Gutenberg-Richter relation taking b ≈ 1 when M < 7. For large earthquakes, M ≥ 7, the seismic data fit Gutenberg-Richter scaling with b ≈ 1.5. If the Gutenberg-Richter scaling for M < 7 earthquakes is extrapolated to larger earthquakes, we would expect a M > 8 earthquake in the study region about every 25 yr. However, our analysis shows a lower frequency of occurrence of large earthquakes so that the expected frequency of M > 8 earthquakes is about 200 yr. The level of seismicity for smaller earthquakes on Taiwan is about 12 times greater than in Southern California and the possibility of a M ≈ 9 earthquake north or south of Taiwan cannot be ruled out. In light of the Fukushima, Japan nuclear disaster, we also discuss the implications of our study for the three operating nuclear power plants on the coast of Taiwan.
An updated and refined catalog of earthquakes in Taiwan (1900–2014) with homogenized M w magnitudes
Earth, Planets and Space, 2016
The main goal of this study was to develop an updated and refined catalog of earthquakes in Taiwan (1900-2014) with homogenized M w magnitudes that are compatible with the Harvard M w. We hope that such a catalog of earthquakes will provide a fundamental database for definitive studies of the distribution of earthquakes in Taiwan as a function of space, time, and magnitude, as well as for realistic assessments of seismic hazards in Taiwan. In this study, for completeness and consistency, we start with a previously published catalog of earthquakes from 1900 to 2006 with homogenized M w magnitudes. We update the earthquake data through 2014 and supplement the database with 188 additional events for the time period of 1900-1935 that were found in the literature. The additional data resulted in a lower magnitude from M w 5.5-5.0. The broadband-based Harvard M w , United States Geological Survey (USGS) M, and Broadband Array in Taiwan for Seismology (BATS) M w are preferred in this study. Accordingly, we use empirical relationships with the Harvard M w to transform our old converted M w values to new converted M w values and to transform the original BATS M w values to converted BATS M w values. For individual events, the adopted M w is chosen in the following order: Harvard M w > USGS M > converted BATS M w > new converted M w. Finally, we discover that use of the adopted M w removes a data gap at magnitudes greater than or equal to 5.0 in the original catalog during 1985-1991. The new catalog is now complete for M w ≥ 5.0 and significantly improves the quality of data for definitive study of seismicity patterns, as well as for realistic assessment of seismic hazards in Taiwan.
Bulletin of the Seismological Society of America, 2004
The observed ground motions from five large aftershocks of the 1999 Chi-Chi, Taiwan, earthquake are compared with predictions from four equations based primarily on data from California. The four equations for active tectonic regions are those developed by Abrahamson . Comparisons are made for horizontal-component peak ground accelerations and 5%-damped pseudoacceleration response spectra at periods between 0.02 sec and 5 sec. The observed motions are in reasonable agreement with the predictions, particularly for distances from 10 to 30 km. This is in marked contrast to the motions from the Chi-Chi mainshock, which are much lower than the predicted motions for periods less than about 1 sec. The results indicate that the low motions in the mainshock are not due to unusual, localized absorption of seismic energy, because waves from the mainshock and the aftershocks generally traverse the same section of the crust and are recorded at the same stations. The aftershock motions at distances of 30-60 km are somewhat lower than the predictions (but not nearly by as small a factor as those for the mainshock), suggesting that the ground motion attenuates more rapidly in this region of Taiwan than it does in the areas we compare with it. We provide equations for the regional attenuation of response spectra, which show increasing decay of motion with distance for decreasing oscillator periods. This observational study also demonstrates that ground motions have large earthquake-location-dependent variability for a specific site. This variability reduces the accuracy with which an earthquake-specific prediction of site response can be predicted.
Natural Hazards, 2000
A better real-time assessment of earthquake effects (i.e. seismic intensity estimation) is crucial for hazard mitigation. Especially during the aftermath of a disastrous event, significant reduction of loss can usually be realized through timely execution of emergency response measures. These effects include strong-ground shaking, ground failure, and their impact on man-made structures. The descriptive Modified Mercalli intensity scale, though still in common use in many poorly instrumented areas of the world, is out of date in areas of extensive strong-motion instrumentation. It is desirable to place the earthquake intensity scale on a more quantitative basis based on the actual recorded ground-motion shaking and carefully compiled damage records. In this paper, we investigated the relationships between earthquake loss, intensity and strong motion peak values, mainly based on the Chi-Chi earthquake. Both the strong-motion peak values and the earthquake loss are related. From the results, we found that peak ground acceleration (PGA) and peak acceleration response spectra at 1 s period (1 s Sa) values are two parameters that give slightly higher correlation coefficients than other parameters for earthquake loss analysis. For intensity estimations, the peak ground velocity (PGV) values and 1 s Sa values are better parameters in the high range and PGA is not stable for smaller earthquakes. Although PGV values give a slightly lower correlation coefficient and larger standard deviation in seismic loss analysis during the Chi-Chi earthquake, it nevertheless gives more reliable instrumental intensity over a broad magnitude range. 1 s Sa is a good parameter for both seismic losses and intensity evaluation. We thus conclude that PGV and 1 s Sa are relatively more stable in damage assessment and, at least in the high end, in intensity estimation. We shall incorporate these findings in our real-time earthquake rapid reporting and early warning systems.
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
Empirical Study of the Frequency and Severity of Earthquakes in Taiwan
The rate at which earthquake occurs in Taiwan was investigated for the period of fifty years (1961 – 2010). The result shows that the study area is characterized predominantly by minor, light and moderate earthquakes with the percentage of strong and major extremely low. The result also revealed that for each magnitude range, the number of shallow focus earthquakes is more than the intermediate focus earthquakes. No deep focus earthquake was observed. The shallow earthquake events with magnitude 4.0-4.9 (light) were the most frequent, followed by 5.0-5.9 (moderate), 3.0-3.9 (minor), 6.0-6.9 (strong) and the least frequent were with magnitude 7.0-7.9 (major). While for intermediate earthquakes, events with magnitude 4.0-4.9 were the most frequent, followed by 3.0-3.9, 5.0-5.9, 6.0-6.9 and the least frequent with magnitude 7.0-7.9. It was also discovered that about three (3) shallow earthquakes occur monthly and about two (2) intermediate earthquakes occur yearly in Taiwan on the average. Furthermore the b-values were calculated for shallow and intermediate focus earthquakes to be 0.80 and 0.74 respectively. The b-values were calculated using the Gutenberg-Richter Relation. The low b-value indicates localized high stresses which are favourable for future rupture.
Seismicity characteristics before the 2003 Chengkung, Taiwan, earthquake
Tectonophysics, 2008
We investigate the variations in seismicity pattern in the Taiwan region before the 2003 Chengkung, Taiwan, earthquake (M w = 6.8) by calculating the standard normal deviate of the Z-values and b-values from the Gutenberg-Richter relation. The Mogi donut-shaped variations in the seismicity can be identified in the Z-value map surrounding the Chengkung earthquake source region. Noticeable decreases in the b-values have also been found around the mainshock region before the Chengkung event. The relatively lowseismicity rate and the decrease in the b-values may be the precursory phenomena associated with the quiescence in overall seismicity and the activation of moderate-sized events occurred around the mainshock region before the Chengkung event.
Earthquake cycle in Western Taiwan: Insights from historical seismicity
Geophysical Journal International, 2009
We attempt at providing new insights about the earthquake behaviour in western Taiwan, based on a comparison between historical information and present-day instrumental records. We provide a consistent picture of the earthquake history during the last four centuries and draw some inferences in terms of seismic cycle. Before instrumental seismic observation in Taiwan started at the end of the 19th century, ancient written earthquake records are available from the ancient Chinese governments and the public concerning the 17th, 18th and 19th centuries. Distribution of casualties and property damage, indicating seismic intensity, can be estimated from archives. Using the Central Weather Bureau (CWB) intensity scale we calibrate the intensity-magnitude relationships from the instrumental seismicity recorded from 1995 to 2005, showing that within the range of historical uncertainties and earthquake depths in western Taiwan, 0-40 km, the depth is not critical in these relationships. With estimated intensities, the magnitudes of historical earthquakes can be evaluated based on a single average empirical relationship between M L , the local magnitude, and I 0 , the epicentral intensity: M L = 0.08I 0 2-0.04I 0 + 3.41. Three types of diagrams are then proposed to describe the historical seismicity. The first type involves simple representation of earthquake events according to time and magnitude. The second type involves cumulative plot of the released elastic energy with time, as calculated from reconstructed magnitudes. The third type of diagram shows the evolution of cumulative seismic strain release with time, based on a Benioff's law indicating that the release of elastic strain related to an earthquake is proportional to the square root of the dissipated energy. These curves highlight inferences of historical seismicity analysis in terms of earthquake frequency and seismic cycle duration in the different segments of the front belt and foreland zones of western Taiwan, with large contrasts suggesting different levels in earthquake hazard.