The waveform inversion of mainshock and aftershock data of the 2006 M6.3 Yogyakarta earthquake

Wiwit Suryanto,Hijrah Saputra,Iman Suardi,Ade Anggraini,Wahyudi Wahyudi

doi:10.1186/s40562-021-00176-w

Abstract

This study comprehensively investigates the source mechanisms associated with the mainshock and aftershocks of the Mw = 6.3 Yogyakarta earthquake which occurred on May 27, 2006. The process involved using moment tensor inversion to determine the fault plane parameters and joint inversion which were further applied to understand the spatial and temporal slip distributions during the earthquake. Moreover, coseismal slip distribution was overlaid with the relocated aftershock distribution to determine the stress field variations around the tectonic area. Meanwhile, the moment tensor inversion made use of near-field data and its Green’s function was calculated using the extended reflectivity method while the joint inversion used near-field and teleseismic body wave data which were computed using the Kikuchi and Kanamori methods. These data were filtered through a trial-and-error method using a bandpass filter with frequency pairs and velocity models from several previous studies. Furthermore, the Akaike Bayesian Information Criterion (ABIC) method was applied to obtain more stable inversion results and different fault types were discovered. Strike–slip and dip-normal were recorded for the mainshock and similar types were recorded for the 8th aftershock while the 9th and 16th June were strike slips. However, the fault slip distribution from the joint inversion showed two asperities. The maximum slip was 0.78 m with the first asperity observed at 10 km south/north of the mainshock hypocenter. The source parameters discovered include total seismic moment M0 = 0.4311E + 19 (Nm) or Mw = 6.4 with a depth of 12 km and a duration of 28 s. The slip distribution overlaid with the aftershock distribution showed the tendency of the aftershock to occur around the asperities zone while a normal oblique focus mechanism was found using the joint inversion.

Highlights

In the early hours of May 27, 2006, at approximately 05.54 local times, an earthquake struck the city of Yogyakarta
The moment tensor inversion obtained using near-field data showed the mainshock fault source parameters of the Yogyakarta earthquake which occurred on May 27, 2006 were strike 218.7°, dip 56.2°, and slip − 61° and discovered to be caused by an oblique fault
The moment tensor inversion for June 8, 9, and 16 aftershocks were calculated using temporary near-field data and the fault source parameters showed the complexity of the Opak fault (Budiman et al 2019; Saputra et al 2018; Anggraini 2013)

Summary

Introduction

In the early hours of May 27, 2006, at approximately 05.54 local times, an earthquake struck the city of Yogyakarta. Several debates on the source are in progress with most researchers reported to have believed the earthquake did not originate from the geological fault along the Opak River due to the distribution of the aftershock towards 10–15 km on the east side (Fukuoka et al 2006; Walter et al 2007; Wulandari et al 2018). Several factors have been indicated by researchers to be influencing this difference, such as the lack of seismometer networks of BMKG which has been existing before 2006, thereby, causing variations in the level of location accuracy, source depth, and fault orientation (Ma and Eaton 2011; Saunders et al 2016)

Methods

Results

Discussion

Conclusion