indoâ€“us workshop on â€œintraplate seismicityâ€ - The CERI Blog

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In India, regional level maps on site conditions are very scarcely available and they are seldom validated with actual field observations. Also, preparing such maps require huge investment, time and efforts in geological and geophysical data acquisition, processing and interpretation. In our study, we have used various field methods for assessing the local site conditions. We have selected sites within the mesoseismal area of the 2001 earthquake to map the shear wave velocity structure of the sites that were intensely liquefied. We also chose sites that were not affected, within the mesoseismal areas. By using Multichannel Analysis of Surface Waves (MASW), passive seismic surveying (Ambient seismic noise recording) and weak and strong motion earthquake data recorded by the permanent seismic stations, we attempt to compute the range of characteristic frequencies and their spatial variations. Here, we present the preliminary results obtained from the MASW and ambient noise surveys carried out during March 2011. We had analyzed MASW data recorded at three distinct site conditions, one at an area of massive liquefaction, second near a hard rock exposure and third in a built-‐up area near Bhuj. Their shear wave velocity profiles correlates well with the variations in the expected lithology. Similarly, the processed H/V ratio curves at the liquefaction site (0.9 Hz) and the built-‐up area (7.04 Hz) show distinct peaks. We have also attempted to derive H/V spectral ratio curve from the Rayleigh wave part of strong motion data recorded at seismic stations on hard rock and alluvium in the Bhuj region. Though the curves did not show very significant difference in the peak frequency, multiple peaks were observed for the alluvium station’s H/V curve.Our preliminary interpretation shows a good correlation between MASW and H/V method in assessing the site condition. This needs to be experimented in all types of site conditions and validated with borehole data. S2-‐P4 Investigations of Mw 5.1 Talala earthquake of October 20, 2011 and aftershocks in Junagadh District in south Saurashtra B.K. Rastogi, Santosh Kumar, Kapil Mohan, Sandeep Aggrawal, Kishan Zala, Vandana Patel & Nagabhushan Rao, Institute of Seismological Research, Gandhinagar 382009 Sumer Chopra, Ministry of Earth Sc, New Delhi Sasangir area of Talala taluka of Junagadh district of Gujarat is experiencing tremors since 2001. The swarm type of earthquake activity in 2001, 2004 and every year from 2007 onwards has occurred after monsoons and lasted 2-‐3 months each time. In 2007 some 200
shocks and in 2011 over 300 shocks down to M1 are well recorded with 1-‐2 km location error. The focall depths are about 2-‐10 km and shocks are accompanied by blast-‐like subterranean sounds. An earthquake of magnitude Mw 5.1 (USGS mb 5.0 and IMD ML 5.0) occurred on 20 Oct 2011. The epicenter (21.09N 70.45E, focal depth 5km) has occurred about 12 km WNW of Talala or 8 km SSW of the 2007 M w 5.0 mainshock epicenter. The epicentral trends deciphered with local networks indicate two // ENE trends (Narmada trend) for about 50km length and a conjugate 15km long NNW trend (Aravali trend). The focal mechanisms by moment-‐tensor analysis of full wave forms of two 2007 Mw4.8 and 5.0 and the 2011 Mw 5.1 tremors indicate rupture along either of the two trends. The ENE trends follow a gravity low between the gravity highs of Girnar mounts. Most of Saurashtra region, as also the Talala area is covered by Deccan Trap Basalt forming plateaus and conical ridges. For the 20/10/2011 Talala earthquake, the MM intensity is estimated to be 6.5. Intensity areas of 6, 5 and 4 and felt distance give Mw 5.1 based on Johnston’s empirical regressions. The source parameters from 14 stations are, Seismic Moment: 16.6 Newton-‐m, Stress Drop: 16 bars, Corner Frequency: 0.62 Hz, Source Radius: 2.3 km. The b and p values are obtained to be low, being 0.67 and 0.71, respectively. Decay rate has been estimated from strong motion recorded at 5 stations from 32 to 200 distance. PGA of 80cm/sec 2 is noted. S2-‐P5 Source parameters and Scaling relations for the earthquakes in Jamnagar region of Gujarat. Santosh Kumar #, Dinesh Kumar* and B.K. Rastogi# # Institute of Seismological Research, Gandhinagar, Gujarat,*Department of Geophysics, Kurukshetra University, Kurukshetra,Corresponding author: The possible scaling and self-‐similarity of small and moderate earthquakes for the Jamnagar, Saurashtra region of Gujarat have been investigated in this study. For this purpose, the source parameters (magnitude, moment, fault dimension, stress drop, corner
Page 1 and 2: INDO-US WORKSHOP ON “INTRAPLATE S
Page 3 and 4: IUSSTF solicits proposals for its a
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Page 7 and 8: The USGS and several agencies of In
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Page 15 and 16: not been a significant earthquake i
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Page 25 and 26: Fig. 2: Seismic activity near the W
Page 27 and 28: Heat flux and crustal temperatures
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Page 49 and 50: Kanter, 1990). The recent 2001 Bhuj

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indoâ€“us workshop on â€œintraplate seismicityâ€ - The CERI Blog