Ruey-Der Hwang

Aspects of characteristics of near-fault ground motions of the 1999 Chi-Chi (Taiwan) earthquake

Abstract In this work, we first study the peak ground accelerations (PGA), the peak ground velocities (PGV) and spectra of acceleration waveforms, based on a coordinate system defined on the focal plane of the earthquake, at nine near‐fault seismic stations along the fault trace. Results show that except for a station, near which there is a remarkable change of the fault trace, the near‐fault PGA value decreases and the PGV value increases from south to north along the fault. Although there exist variety and complexity in near‐fault acceleration spectra, some substantial conclusions can still be retrieved. The source and site effects are two major factors in controlling the variation in near‐fault acceleration spectra along the fault. The site effect acts mainly on the high‐frequency spectra, while the source effect on low‐frequency ones. For the three components, the value of the predominant frequency is, on the average, higher in the hanging wall than in the foot wall.

Rupture features of the 2010 Mw 8.8 Chile earthquake extracted from surface waves

This study used the rupture directivity theory to derive the fault parameters of the 2010 Mw 8.8 Chile earthquake on the basis of the azimuth-dependent source duration obtained from the Rayleigh-wave phase velocity. Results revealed that the 2010 Chile earthquake featured asymmetric bilateral faulting. The two rupture directions were N171°E (northward) and N17°E (southward), with rupture lengths of approximately 313 and 118xa0km, respectively, and were related to the locking degree in the source region. The entire source duration was approximately 187xa0s. After excluding the rise time from the source duration, the northward rupture velocity was approximately 2.02xa0km/s, faster than the southward rupture velocity (1.74xa0km/s). On average, the rupture velocity derived from this study was slower than that estimated from finite-fault inversion; however, several historical earthquakes in the Chile region also showed slow rupture velocity when using low-frequency signals, as surface waves do. Two earlier studies through global-positioning-system data analysis showed that the static stress drop of 50–70xa0bars for the 2010 Chile earthquake was higher than that for subduction-zone earthquakes. Hence, a remarkable feature was that the 2010 Chile earthquake had a slow rupture velocity and a high static stress drop, which suggested an inverse relationship between rupture velocity and static stress drop.Graphical abstract.