The Composite Source Model for Broadband Simulations of Strong Ground Motions

2014 ◽  
Vol 86 (1) ◽  
pp. 68-74 ◽  
Author(s):  
J. G. Anderson
Keyword(s):  
Ground Motions ◽  
Source Model ◽  
Strong Ground Motions ◽  
Composite Source Model ◽  
Strong Ground

Strong ground motion from the Uttarkashi, Himalaya, India, earthquake: Comparison of observations with synthetics using the composite source model

1995 ◽  
Vol 85 (1) ◽  
pp. 31-50 ◽  
Author(s):  
G. Yu ◽  
K. N. Khattri ◽  
J. G. Anderson ◽  
J. N. Brune ◽  
Y. Zeng
Keyword(s):  
Ground Motions ◽  
Source Model ◽  
Seismic Gap ◽  
Main Central Thrust ◽  
Strong Ground Motions ◽  
Velocity Models ◽  
Horizontal Acceleration ◽  
Peak Horizontal Acceleration ◽  
Composite Source Model ◽  
Strong Ground

Abstract The Uttarkashi earthquake of 19 October 1991 (MS = 7.0) occurred in the greater Himalayan region north of the main central thrust, at an estimated depth of 12 km. The fault plane solution indicates a low-angle thrust mechanism, striking northwest, consistent with the tectonic pattern of thrusting in the region. Aftershocks define a belt parallel to, and north of, the surface trace of the main central thrust, roughly 10-km wide and 30-km long. The mainshock is located at the northeast edge of this zone. The earthquake was recorded on 13 strong-motion accelerographs at distances ranging from 25 to 150 km from the epicenter. One station at Bhatwari (peak horizontal acceleration of 272 cm sec−2) is above the aftershock zone. The maximum peak horizontal acceleration was about 313 cm sec−2 at Uttarkashi, at an epicentral distance of 36 km. The amplitudes and frequency content of the strong ground motions are more or less consistent with expectations for an earthquake of this magnitude in California. Synthetics generated using the composite source model and synthetic Green's functions (Zeng et al., 1994a, b) are successful in producing acceleration, velocity, and displacement with a realistic appearance and the correct statistical properties of the two accelerograms recorded nearest the fault (Bhatwari and Uttarkashi). To produce these, we introduced trial-and-error modifications of the layered-medium velocity model within uncertainties. At more distant stations, we first used the velocity structure that worked for the two nearest stations. Differences emphasize the large potential role of unknown site and wave-propagation effects. For the station at Tehri, we explored different velocity models, and found one there that was also quite successful. We then used these two velocity models to predict strong ground motions at Bhatwari and Tehri, from a potential magnitude 8.5 earthquake filling part of the seismic gap along the Himalayan frontal faults. The synthetics show peak accelerations that are only somewhat larger than those in the Uttarkashi event, but much longer durations and increased amplitudes of response spectra at long periods.

Source model of the 1995 Hyogo-Ken Nanbu earthquake and simulation of near-source ground motion

1998 ◽  
Vol 88 (2) ◽  
pp. 400-412
Author(s):  
Katsuhiro Kamae ◽  
Kojiro Irikura
Keyword(s):  
Ground Motion ◽  
Stress Drop ◽  
Ground Motions ◽  
Source Region ◽  
Source Model ◽  
Rupture Directivity ◽  
Strong Ground Motions ◽  
Starting Point ◽  
Initial Source ◽  
Strong Ground

Abstract The 1995 Hyogo-Ken Nanbu earthquake struck the heavily populated Kobe and adjacent cities in western Japan. More than 6400 people were killed, and more than 150,000 buildings were destroyed. The characteristics of mainshock ground motions in the heavily damaged area are needed to understand how buildings and bridges performed and why they reached failure. Unfortunately, very few strong ground motions were recorded in the heavily damaged area during the mainshock. In this study, we attempt to estimate mainshock ground motions by using the empirical Green's function method (EGF method). First, we assume an initial source model with the asperities based on the rupture process obtained by inversion of strong-ground-motion records. For simplicity, we consider each asperity as a subevent with uniform stress drop in a finite extent. Then, the initial model was improved by matching the synthetic and observed ground motions using a trial-and-error procedure. The final model consists of three subevents: subevent 1 with stress drop of 163 bars, under the Akashi Strait around the rupture starting point; subevent 2 with stress drop of 86 bars, under the Nojima Fault in Awaji Island; and subevent 3 with stress drop of 86 bars, under Kobe. Finally, we estimate strong ground motions using aftershock records at sites where the mainshock was not recorded. The near-source motions in Kobe synthesized with the best-fit model are characterized by two large pulses with a duration of 1 to 3 sec. The pulses are caused by forward rupture directivity effects from subevents 1 and 3. Peak horizontal acceleration and velocity of the synthesized motions at the heavily damaged sites are about 1000 cm/sec2 and 130 cm/sec, respectively, while those at a rock site in the near-source region are about 300 cm/sec2 and 60 cm/sec.

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