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.
This study comprehensively investigates the source mechanisms associated with the mainshock and aftershocks of the Yogyakarta earthquake of magnitude Mw = 6.3 on May 27, 2006. Therefore, this study is to provide a more precise answer to the controversial source mechanism. This study uses moment tensor inversion to obtain fault plane parameters and joint inversion to obtain spatial and temporal slip distributions during an earthquake. The coseismic slip distribution is overlaid with the relocated aftershock distribution to see the stress field variations around the tectonic area of the study. Moment tensor inversion uses near-field data, and joint inversion uses near-field and teleseismic body wave data. The data is filtered by trial and error using a bandpass filter with frequency pairs and velocity models from several previous studies. The green's function for moment tensor inversion calculated using the extended reflectivity method and joint inversion computed using the Kikuchi and Kanamori methods. In this study, we apply the Akaike Bayesian Information Criterion (ABIC) method to obtain more stable inversion results. The results of the mainshock and aftershock moment tensor inversion show different fault types. The mainshock fault types are strike-slip and dip-normal types, while the 8th aftershock is of the same type as the mainshock, while the 9th and 16th June are strike slips. The joint inversion results show two asperities. The maximum slip is 0.78 m, with the first asperity 10 km south of the mainshock and the second asperity 10 km north of the mainshock. The obtained source parameters are total seismic moment M0 = 0.4311E + 19 (Nm) or Mw = 6.4, with a source depth of 12 km and a source duration of 28 seconds. Slip distribution overlay with aftershock distribution shows compatibility. The type of focus mechanism that results from this joint inversion is the oblique.
This research was examines the focal mechanism associated with the mainshock and three aftershocks of the magnitude 6.3 Yogyakarta earthquake on May 27, 2006. This study, therefore, aims to provide a cleareranswer on the source mechanism of the earthquake, which has been debated. Data were obtained from the mainshock and aftershock sources, on June 8, 9, and 16, 2006. The mainshock and three aftershocks were used to conduct waveform inversion by calculating the Green's functions through the extended reflectivity method of the near-field and the far-field signal component. The mainshock's focal mechanism has a strike, dip, and range angle of 243.40o, 77.50o, and -28.30o, respectively.Furthermore, the mainshock is not a pure strike-slip as previously hypothesized. The focal mechanism for the aftershock earthquake source on Mw 4.4, obtained on June 8, had a strike, dip, rake, and variance of 192.20o, 29.70o, -48.30o and 0.22, respectively. This aftershock had a different segment from the mainshock event and those obtained on the 9 and 16 of June with the same type of faulting as the mainshock with variance values of 0.195 and 0.243. These results showed that the mainshock of May 27, 2006, activated the aftershock on June 8, with a different type of fault.
Research on the analysis of the source mechanism of the mainshock and aftershock events of the May 27, 2006, Yogyakarta earthquake, which is thought to have originated from the Opak fault and analysis of receiver function data to model the subsurface velocity P of the Central Java subsurface, to obtain a geological form model of the Opak fault. This research aims to support the development of the Yogyakarta Aerothroppolis area in terms of disaster analysis. The data used in this study are remote Teleseismic receiver function data from the MERAMEX station installed in 2004, and data for the Bantul earthquake event and its aftershock event in 2006. The results obtained from the analysis are that the Yogyakarta area is shaped like a half-graben close to Yogyakarta International Airport. The fault that separates the western part of Yogyakarta is still not identified. Based on the results of the rupture process analysis of the source along the Opak fault plane, some zones have not yet released their energy. The distribution of aftershocks due to the mainshock on 27 May 2006 is spread around the Opak fault, which is heading North-South, and West-East, which is thought to have activated the minor fault to the east of the Opak fault. The opak fault rupture area can be analyzed to have a Low Anomaly velocity P value from the receiver function data and is the same as the aftershock event obtained.
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