scholarly journals The Waveform Inversion of Mainshock and Aftershock Data of the 2006 M6.3 Yogyakarta Earthquake

2020 ◽  
Author(s):  
Hijrah Saputra ◽  
Wahyudi Wahyudi ◽  
Iman Suardi ◽  
Wiwit Suryanto
Keyword(s):  
Focal Mechanism ◽  
Green’S Functions ◽  
Near Field ◽  
Waveform Inversion ◽  
Strike Slip ◽  
Earthquake Source ◽  
Source Mechanism ◽  
Far Field ◽  
Signal Component ◽  
Reflectivity Method

Abstract 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.

Co-seismic internal deformations in a spherical layered earth model

2020 ◽  
Vol 221 (3) ◽  
pp. 1515-1531
Author(s):  
Tai Liu ◽  
Guangyu Fu ◽  
Yawen She ◽  
Cuiping Zhao
Keyword(s):  
Green's Functions ◽  
Green’S Functions ◽  
Near Field ◽  
Earth Model ◽  
Coulomb Stress ◽  
Far Field ◽  
Coulomb Stress Changes ◽  
Layered Earth ◽  
Stress Changes ◽  
Internal Deformation

SUMMARY Using a numerical integral method, we deduced a set of formulae for the co-seismic internal deformation in a spherically symmetric earth model, simultaneously taking self-gravitation, compressibility and realistically stratified structure of the Earth into account. Using these formulae, we can calculate the internal deformation at an arbitrary depth caused by an arbitrary seismic source. To demonstrate the correctness of our formulae, we compared our numerical solutions of radial functions with analytical solutions reported by Dong & Sun based on a homogeneous earth model; we found that two sets of results agree well with each other. Our co-seismic internal Green's functions in the near field agree well with the results calculated by the formulae of Okada, which also verifies our Green's functions. Finally, we calculated the Coulomb stress changes on the Japanese Islands and Northeast China induced by the Tohoku-Oki Mw 9.0 earthquake using the methods described above. We found that the effect of layered structure plays a leading role on the near field, while curvature occupies a dominant position on the deep region of the far field. Through a comparison of the Coulomb stress changes at a depth of 10 km on a layered earth model calculated by our method along with the corresponding results of Okada, we found that the discrepancy between them in near field was ∼31.5 per cent, and that of far field was >100 per cent of the signals.

Study on the layout of GNSS sites for strike-slip faults

2019 ◽  
Vol 219 (2) ◽  
pp. 1131-1137
Author(s):  
Zhenyu Zou ◽  
Zaisen Jiang ◽  
Yueju Cui ◽  
Long Zhang ◽  
Peng Wang ◽  
...  
Keyword(s):  
Profile Analysis ◽  
Near Field ◽  
Slip Rate ◽  
Strike Slip ◽  
Deformation Curve ◽  
Far Field ◽  
Seismogenic Layer ◽  
Dense Distribution ◽  
Xiaojiang Fault ◽  
Equal Spacing

SUMMARY In the profile analysis of faults, the distribution of GNSS sites directly affects the accuracy of the results of slip rate and locking depth. This paper discusses strategies for designing the layout of GNSS stations perpendicular to strike-slip faults in terms of site spacing and the Minimum Effective Distance, which is 20 times the locking depth of the fault. Three layout models are proposed considering the complexity of strike-slip faults: (1) Equal spacing layout, in which many stations are deployed in the far field, only a few are deployed in the near field. (2) Equal deformation layout, in which stations are densely arranged in the near field and sparsely arranged in the far field according to the frequency of deformation curve. (3) Equal slope spacing layout, in which stations are arranged according to the nonlinear degree of the deformation curve, with dense distribution in regions with high nonlinearity and sparse distribution in approximately linear regions. The three models were used to redistribute the sites in the Qiaojia to Dongchuan segment of the Xiaojiang fault profile, and their performances were compared with that of the current sites distribution of the segment. The results showed that model 1 is optimal for fitting the accuracy of slip rate and model 3 is optimal for the accuracy of locking depth. Overall, model 3 appears to be the best choice, considering that the accuracy of the locking depth is more difficult to control. One of the main purposes of deployment is to identify the seismogenic depth of the fault. With the locking depth of the fault gradually approaching the depth of the seismogenic layer during an interseismic period, the accuracy of observations of sites deployed at a preset value of historical seismogenic depth of the fault would improve.

Focal mechanism determination and identification of the fault plane of earthquakes using only one or two near-source seismic recordings

1999 ◽  
Vol 89 (6) ◽  
pp. 1558-1574 ◽  
Author(s):  
Bertrand Delouis ◽  
Denis Legrand
Keyword(s):  
Focal Mechanism ◽  
Fault Plane ◽  
Epicentral Distance ◽  
Near Field ◽  
Waveform Inversion ◽  
Strong Motion ◽  
Source Model ◽  
Resolving Power ◽  
Fault Parameters ◽  
Single Station

Abstract A waveform inversion scheme was developed in order to explore the resolving power of one or two seismic recordings at short epicentral distance for the determination of focal mechanisms and the identification of the fault plane of earthquakes. Two key features are used to constrain the fault parameters with a reduced number of stations: (1) a simple finite-dimension source model and (2) the modeling of the complete displacement field, including the near-field waves. The identification of the fault plane should be possible, even with a single station, as soon as the seismograms produced by the two nodal planes of a same focal mechanism are significantly different, which is the general case when waveforms are controlled by source finiteness. Seven parameters, including the strike, dip, rake, and dislocation, are explored with a grid search, and the minima of the misfit error between the observed and calculated seismograms are mapped. With such an approach, it is possible to conclude about the uniqueness or nonuniqueness of the solutions. The method is tested with three earthquakes of moderate to large size for which the fault plane is well established and for which strong-motion records are available at maximum distances of a few tens of kilometers. Test events are the 1994 Northridge (Mw = 6.7, California), the 1996 Copala (Mw = 7.3, Mexico), and the 1996 Pinotepa Nacional (Mw = 5.4, Mexico) earthquakes. In the case of inversions with two stations, we find a unique solution, or a group of similar solutions, with a good estimation of the focal mechanism and the proper selection of the fault plane. Our results also show that in some cases a single station may be enough to recover the fault parameters. The inversion scheme presented here may be systematically applied to future earthquakes, especially to those recorded by few stations. It should be particularly useful in the case of blind faults for which the fault plane may not be identified with the help of other data.

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