Simulation of 2003 Bam (Iran) Earthquake Using Empirical Green’s Function Method Via Very Small and Near-Fault Events

riahi, ali ; sadeghi, hossein ; hosseini, sayyed keivan;

The 2003 Bam, Iran, earthquake (Mw = 6.6) was recorded by the BAM accelerometer station. Since the causative fault was located just below the city, the accelerometer recorded the main shock, a foreshock and several local aftershocks. To study the scenario of rupturing, we simulated all components of the observed main shock waveform via the empirical Green’s function method. 28 selected aftershocks and the single foreshock are used to simulate the main
shock in the frequency range of 0.5–5 Hz. Since the events were very close to the station, some small events may not have similar path effects to the main shock. Therefore, it is essential to employ some appropriate changes to the waveforms to alleviate path difference effects. The starting point of the rupture is identified in the centre of the strong motion generation area and is located approximately 5 km south of the BAM station and in depth of about 7 km. The horizontal simulated components imply that the main shock was located west of
the BAM station. In contrast, significant variation in the ratio of amplitudes in EW and NS components may be used to discuss the possibility of dissimilarity in the focal mechanism of the small events. Most aftershocks with similar mechanisms to the main shock, that is
similar EW/NS maximum amplitude ratio, have capacity to simulate certain peaks of their horizontal components. However, some small events with different mechanisms are only able to simulate the peaks of up to one horizontal component. Some changes were applied to
the empirical Green’s function method to incorporate two small events by using a combined fault model. While the two aftershocks have different mechanisms, some combinations may improve simulations. The rupture initiating point at the middle of the fault plane and improved
simulations by combination of two fault surfaces with different focal mechanisms may suggest a bilateral rupture and combination of two focal mechanisms for the main shock of the Bam earthquake.