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Joint Study of Source Parameters of Small to Moderate Earthquake

Author: WangZhenJie
Tutor: NiSiDao
School: University of Science and Technology of China
Course: Solid Earth Physics
Keywords: Focal mechanism Focal depth Joint inversion CAP method InSAR sPL Surface wave dispersion
CLC: P315.3
Type: Master's thesis
Year: 2011
Downloads: 75
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Abstract

Accurate determination of the source parameters (seismic moment, depth, strike, dip and slip angle) to understand the seismotectonic, ground motion simulation has important significance. M5.5 - 6.5 magnitude earthquake, can be a good use of the point source approximation. Its far-field waveform with a higher signal-to-noise ratio, and the global station network can be recorded to the teleseismic depth phases the sP or a pP usually can be used to determine the focal depth, due to teleseismic waveform from source angle is small, the ball of the focal sampling areas are mainly concentrated in the central part of the fault dip constraint. To this end, we have developed a joint inversion algorithm comprehensive utilization of near-field and far-field waveform data joint inversion of focal depth and focal mechanism solutions. Zhao and Helmberger 1994 was used for inversion of focal mechanism solutions and depth CAP method, we add the far-field waveform data, and near-field and far-field waveform data given to changes in the weights of the inversion of source parameters. We studied the seismic events with the geometric parameters of the different fault. First, based on the near-field and far-field waveforms using the CAP method to study the July 11, 2004 the Ms6.6 level and the Ms6.6 level of April 7, 2005 of Zhongba earthquake in Tibet source parameters obtained by comparing field and far-field waveform inversion of source parameters of different sensitivity. Then combined near-field far-field waveform inversion twice earthquake focal mechanism and focal depth. Comprehensive utilization of magnitude than the information, including the expansion of the P wave and surface-wave part of the near-field, Rayleigh waves and Love waves part, far-field P-wave and SH wave the part, CAPjiont method to get a stable and reliable mechanism solutions; comprehensive utilization of nearly the field depth phases such as sPL, sPg, sPn, far-field the depth depth phases (SP, pP) and free surface reflected SH wave shock equal CAPjiont method to get a stable and reliable focal depth. Hi-Climb broadband waveform data at the same time due to the high quality, we adopt CAPloc inversion some aftershocks of the the Zhongba two earthquakes focal mechanism and depth. The results showed that the main shock and aftershocks mechanisms underlying normal fault, part strike slip slightly, roughly north-south direction, indicating that the plateau intraplate things to tensile, in line with the structure of the regional background. Earthquake sequence in the research, the deepest focal depth of 14km, the most shallow 3km. To display the brittle cap rock of the shallow crust in the region, in line with the distribution of earthquakes in the Tibetan Plateau board. M6.0-6.5 earthquake relatively strong earthquakes M gt; 7.0 earthquake is more frequent, usually given point source approximation can be well described by seismological methods to obtain focal mechanism solutions can seismogenic fault have a good understanding. The more detailed the source process, like finite fault simulation, only through the far-field waveform data to define M lt; slip of the fault scale of the 7.0 magnitude earthquake on the fault plane, and its resolution is difficult to achieve the required accuracy, and analysis of the higher frequency of seismic waveform often can not ignore the impact of the three-dimensional velocity structure in the absence of good velocity model the credibility inversion results. Lack of near-field ground strong motion data, relatively speaking, far-field waveform record is not sensitive to static spatial distribution of slip. Geodetic and remote sensing techniques, such as InSAR, GPS and optical images can provide additional surface static deformation field, and more and more is applied to the seismic study up. Zhongba two main shock, further C-band Envisat satellite-based European Bureau observed before and after the four SAR image to obtain the the Zhongba earthquake coseismic deformation, sensitive iterative fitting algorithm (Senstitive-BasedIterative Fitting, SBIF) inversion slip distribution of the Zhongba two earthquake fault plane. The research results show that the 2004 the Zhongba earthquake faults along the strike and down-dip direction rupture scale of 16km × 16km. The 2005 the Zhongba earthquake fault ruptured scale 27.5km × 17.5km. To better understand the two earthquake fault rupture surface, part of the two earthquakes aftershocks relocation. Geodesy and seismology results showed good agreement, the results show that the two earthquakes rupture surface contiguous, there is no overlap phenomenon. InSAR results also show that the 2004 the Zhongba earthquake epicenter locations for 83.75E, 30.66N the Zhongba earthquake epicenter location to 83.73E, 30.52N difference of about 15 km, two earthquakes. The same time in 2004 the Zhongba earthquake fault rupture slippage centroid position depth of 9.7km, the the CAP inversion focal depth of 10km. Centroid position of the amount of slip in the 2005 the Zhongba earthquake fault on the depth of 6.4km, the the CAP inversion of the focal depth of 6km. InSAR results and CAP results show good agreement. Based the near earthquake CAP method, adding far shock body waveform data, comprehensive a near earthquake teleseismic waveform data joint inversion of Panzhihua, Sichuan province August 30, 2008 - Huili the Ms6.1 earthquake focal mechanism solutions and focal depth. And epicentral distance of about 38km Panzhihua station sPL of phases, using waveform fitting, the single determine the focal depth of the main shock and aftershocks. The results show that the faulting mainshock mechanism sinistral strike slip slightly Chairman thrust component, one of the nodal planes toward 194 °, dip angle of 78 °, the sliding angle 12 °, consistent with Yuanmou - the green juice Jiang fracture geometry. The best-fit depth of the main shock the CAP method and sPL of established mutual agreement with the 11km. The the aftershocks focal depth research mainly concentrated in the 11km and 16km depth near the earthquake focal depth in the seismogenic zone with good coordination. We infer that the the Panzhihua earthquake sequence belongs on the brittle layer of the crust earthquake earthquake zone brittle - ductile transition zone starts at 17km depth of. By the opposite wave analysis in Chapter VII, to recognize October 9, 2007, in the southwest of earthquake activity with Australia Katanning earthquake as a shallow earthquake, the focal depth shallower than 1km, based on surface wave dispersion curves obtain the velocity structure of the source region and relatively reliable focal mechanism of the simple one-dimensional layered model. The by full waveform fitting, to determine the focal mechanism of 54.4 ° / 44.0 ° / 131 °. Further analysis of surface wave to obtain the S-wave layered velocity model to simulate the InSAR measured coseismic deformation. Based on the the Okada fault model parameters, including strike, dip, depth, length and width of the center position, and slip. Based on the InSAR measured deformation field, adjusting the source parameters, forward calculation. When the focal depth of 0.35km, across the earthquake zone 4 displacement profiles to simulate the deformation field and InSAR measured deformation field are in good agreement. The seismology get moment magnitude Mw of 4.5 moment magnitude Mw4.7 InSAR get to keep some differences may be due to the rapid postseismic deformation caused by 36.9% thanks to postseismic deformation of InSAR detection of seismic moment. Reason may be extremely shallow source at the weathering the caprock or red soil viscoelastic relaxation, or dominated by extremely shallow source at the pore rebound effect, or afterslip also be linked to specific mechanisms to be further research. Surface deformation and seismic activity, by several different methods to measure and measurement, such as seismology, radar and optical remote sensing, geodesy, field surveys, etc. to study earthquakes, although each method has advantages but none fully able to explore all aspects of the earthquake process. Other surface deformation measurement method which can take, such as Global Navigation Satellite System (GNSS), synthetic aperture radar interferometry technique (InSAR) and sub-pixel technology (SCT), the study of earthquakes. Joint research, joint research on the source parameters of multiple means including seismology different methods of joint research and seismological and non-seismological methods is very necessary.

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CLC: > Astronomy,Earth Sciences > Geophysics > Earth ( rock circles ) physics ( geophysics ) > Seismology > Seismic waves, earthquake magnitude,source physical
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