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Hwang, L.J., 1991

Teleseismically determined source parameters of several large collision-zone earthquakes

Bibliographic Reference

Hwang, L.J., 1991, Teleseismically determined source parameters of several large collision-zone earthquakes: Pasadena, California, California Institute of Technology, Ph.D. dissertation, 204 p.


Understanding earthquake hazards begins with the understanding of the earthquake process itself and its effects in the near source region. Here both ends of the problem are explored. First, source parameters and rupture models for several earthquakes around the circum-Pacific are studied. Second, acceleration spectra are compared to teleseismic data. It is hoped that the extensive teleseismic data base can be used to scale acceleration spectra for large future, earthquakes. The 7 May 1986 Andreanof Islands earthquake was a large (1.3 x 1028 dyne-cm) thrust event (strike 257°, dip 18°, rake 116°) that ruptured a 220 km segment of the Aleutian Arc. The earthquake ruptured bilaterally with the largest moment releasing subevent nucleating 75 - 90 km west of the epicenter in a region of low aftershock seismicity. At a distance of 100 km, the acceleration spectrum had the same amplitude as that from teleseismic data. The 20 May (6.4 Mrm s, NEIC) and 14 November (7.3 Mrm s, 1.7 x 1027 dyne-cm) 1986 Hualien earthquakes occurred on two steeply dipping, reverse faulting events near the Eurasian-Philippine Sea plate boundary. The amplitude of the observed spectra at a distance of 70 - 80 km is 5 times that from teleseismic data. This is consistent with previous observations. Comparisons between hard and soft rock recording sites indicate that the alluvial valley amplified the strong ground motion between 0.15 - 1.8 Hz. The 24 November 1987 Superstition Hills earthquake (8 x 1025 dyne-cm) consisted of two spatially distinct subevents with different focal mechanisms at depths between 4 to 8 km. Rupture models along with aftershock, afterslip and geologic data suggest that the northern and southern segments of the Superstition Hills fault behaved differently during this event. The 1987-88 Gulf of Alaska earthquake sequence consisted of three large, intraplate, strike-slip earthquakes (7.2, 7.8, 7.7 Mrm w), whose depths extended to 25 km. The data are modeled with multiple subevents with different focal mechanisms. In comparison with other large events, the short durations and rupture lengths of the two largest events illustrate the difference in strength between oceanic and continental lithosphere. Moment release is confined to the epicentral region and/or regions of apparent structural complexities where seismicity trends intersect.

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