Abstract Database


Siti Norbaizura MAT SAID
Supervisor: Tatsuhiko HARA
Country: Malaysia

Since November 30, 2007, small local earthquakes have been observed in the Malay Peninsula near the Bukit Tinggi area. The total number of these events in the Malay Peninsula is 30 until the end of 2010, including the newly recorded small earthquakes in Jerantut, Manjung and Kuala Pilah, which occurred in March, April and November in 2009, respectively. Although hypocenters and magnitudes are determined for these events using data from the Malaysian National Seismic network, focal mechanisms have not been determined. In this study, we determined their focal mechanisms. We selected three crust structure models, and compared the observed travel time differences between P and S waves to those computed for these models. Although they agree relatively well for all of these models, model iasp91 explained the observations better. We analyzed four events that occurred in the Bukit Tinggi area for focal mechanism determination. We used three-component broadband waveform data recorded at stations IPM and KOM of the Malaysian National Seismic network. We determined their focal mechanisms using polarity data of the first motions of P and S waves and their amplitude ratios. We used iasp91 for take off angle calculations. We obtained relatively well-constrained solutions for all four events. The focal mechanisms of the largest 3.5mb event, which occurred on November 30, 2007 is a mostly strike slip with some dip slip mechanism, while those of three events are strike slip mechanisms. The maximum compressional (P) axes of the November 30, 2007 event is in the NNW-SSE direction, while those of three events are in the NW-SE direction. The minimum compressional (T) axes of the strike slip events are in the NE-SW direction. Since there is no surface trace of ruptures observed, this result is important to improve our understanding of these seismic activities.