IDENTIFYING STRONG-MOTION GENERATION AREAS OF THE 2007 Mw8.0 PISCO, PERU, EARTHQUAKE
USING THE EMPIRICAL GREEN’S FUNCTION METHOD
Supervisor: Toshiaki YOKOI, Takumi HAYASHIDA
This study identified the regions of the rupture areas of the Mw8.0 August 15, 2007 Pisco, Peru Earthquake able of simulating the strong ground motion. We determined strong motion generation areas (SMGA) and rise time for the earthquake, using the empirical Green’s function method (EGFM) in the frequency range between 0.1 and 1 Hz at seismic stations MOL and PRC.
As an initial approach, we applied the criteria of Somerville et al. (1999) to model the SMGAs, coincident with the proposed asperity model. The source model consists of two subevents, suggested by the observed seismic waveforms and finite-source rupture model. For calculation, we assumed the observed records of two small aftershocks (Mw5.6 and Mw5.0) as empirical Green’s functions (EGF). The observed waveforms of the mainshock were divided in two wave packets to compute the contribution from each SMGA independently. The acceleration spectra analysis of each wave packet and aftershocks did not follow the omega-squared source spectra model, indicating the difficulty of applying the source spectra ratio fitting method (SSRF) and neither was it possible to obtain the scaling factors N and C.
Finally, the SMGAs (SMGA1 and SMGA2) were obtained by a grid searching, considering correlation coefficients and visual comparisons between the successive observed and synthetic waveforms. The grid search includes the scaling factor N and the starting rupture point. The C value was tuned in by visual comparisons. The agreement between the observed and synthesized waveforms from SMGA2 were poor, compared with those for SMGA1. The poor resolution might be due to the biased distribution of the few stations, as well as the complexity of the source rupture propagation. On the other hand, source area and amount of average slips for asperities followed the scaling laws for interplate earthquakes.