Simultaneous estimation of earthquake source parameters and crustal Q value from broadband data of selected aftershocks
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is paper presents the simultaneous estimation of source parameters and crustal Q values for small to moderate-size aftershocks (Mw 2.1–5.1) of the Mw 7.7 2001 Bhuj earthquake. The horizontal-component S-waves of 144 well located earthquakes (2001–2010) recorded at 3–10 broadband seismograph sites in the Kachchh Seismic Zone, Gujarat, India are analyzed, and their seismic corner frequencies, long-period spectral levels and crustal Q values are simultaneously estimated by inverting the horizontal component of the S-wave displacement spectrum using the Levenberg–Marquardt nonlinear inversion technique, wherein the inversion scheme is formulated based on the ω-square source spectral model. The static stress drops (Δσ) are then calculated from the corner frequency and seismic moment. The estimated source parameters suggest that the seismic moment (M0 ) and source radius (r ) of aftershocks are varying from 1.12 × 1012 to 4.00 × 1016 N-m and 132.57 to 513.20 m, respectively. Whereas, estimated stress drops (Δσ) and multiplicative factor (Emo ) values range from 0.01 to 20.0 MPa and 1.05 to 3.39, respectively. The corner frequencies are found to be ranging from 2.36 to 8.76 Hz. The crustal S-wave quality factor varies from 256 to 1882 with an average of 840 for the Kachchh region, which agrees well with the crustal Q value of the seismically active New Madrid region, USA. Our estimated stress drop values are quite large compared to the other similar size Indian intraplate earthquakes, which can be attributed to the presence of crustal mafic intrusives and aqueous fluids in the lower crust as revealed by the earlier tomographic study of the region.
1. Introduction The 2001 Bhuj earthquake of Mw 7.7 is one of the largest intraplate earthquakes in recent time, which claimed a death toll of 20,000 people. This earthquake (lat. 23.412◦ N and long. 70.232◦ E) took place on 26th January 2001 along a south dipping reverse fault at 23 km depth in the Kachchh rift zone, which is situated in the northwestern corner of peninsular India (Mandal et al. 2004a, 2004b). The maximum intensity was reported to be X+ on MM
scale (Rastogi et al. 2001). Within a span of 192 yrs (1819–2011), two large intraplate earthquakes, viz., the 1819 Kachchh (Mw 7.8) and the 2001 Bhuj (Mw 7.7) have occurred in the Kachchh region. These earthquakes caused widespread destruction of properties and casualties (at least 22,000 people). In spite of such devastation, the earthquake hazard assessments for various seismogenic zones of India have grossly been undermined. Under these circumstances, it is proposed here to analyze the source parameters from the recorded aftershock
Keywords. Earthquake source parameters; crustal Q-value; simultaneous inversion; S-wave spectra; aftershocks. J. Earth Syst. Sci. 121, No. 6, December 2012, pp. 1421–1440 c Indian Academy of Sciences
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data of Bhuj earthquake from Kachchh region of Gujarat province, India to properly assess the earthquake hazard of the region. The 2001 Bhuj earthquake is perhaps on
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