Characterizing site response in the Attock Basin, Pakistan, using microtremor measurement analysis
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ORIGINAL PAPER
Characterizing site response in the Attock Basin, Pakistan, using microtremor measurement analysis S. M. Talha Qadri 1,2 & Md. Aminul Islam 1 & M. R. Shalaby 1 & Khaista Rehman Khattak 3 & S. H. Sajjad 2
Received: 22 June 2015 / Accepted: 5 June 2017 # Saudi Society for Geosciences 2017
Abstract The Attock Basin is situated close to the northwest of Pakistan. Recent seismic event of October 2015 (7.5Mw) near the Pakistan Afghanistan border has proved that the area of interest is seismically active and triggered a series of aftershocks of magnitude even greater than 6.5Mw. This seismic activity has posed danger to the future of the people and infrastructure especially to the northwestern part of the country. Therefore, site response analysis is essential for estimating local site conditions in response to seismic events. Ambient noise recordings were made at 50 sites within urban and semiurban settlements in the Attock Basin to analyze the site response of the small but densely populated basin. At each of these sites, the fundamental frequency of the soft sediments (f0), the amplitude (A0) of corresponding H/V spectral ratios, the thickness of soft sediment (H) lying over competent lithology, and the soil vulnerability index (Kg) were studied. Results were correlated with sparsely available borehole data to enhance the credibility of the study conducted for microzonation and predicting the site response to earthquake seismicity in the Attock Basin. The soil vulnerability index was found to range from moderate to high. Results clearly showed that the study area exhibits low to moderate fundamental frequency with greater soft sediment thicknesses distributed throughout the
* S. M. Talha Qadri [email protected]
1
Faculty of Science, Physical and Geological Sciences, Universiti Brunei Darussalam, Jalan Tungku Link, Gadong BE1410, Brunei Darussalam
2
Department of Earth Sciences, University of Sargodha, Sargodha, Pakistan
3
National Center of Excellence in Geology, University of Peshawar, Peshawar, Pakistan
study area. Moreover, higher impedance contrasts were found at most of the sites within the central part of the Attock Basin, thus reflecting a moderate to high susceptibility of damage in those regions in response to seismic events. Keywords Site response analysis . Ambient noise . Fundamental frequency . H/V spectral ratio . Impedance contrast
Introduction Pakistan is susceptible to various natural disasters. It has encountered earthquakes, floods, droughts, and landslides as a consequence of its unstable geological setting. Few recently recorded seismic events of magnitude 7.0 or more have jolted the entire country resulting in infrastructural devastation and heavy death tolls. October 2015 Hindu Kush earthquake (7.5Mw) is an example of one of such events which have posed severe threat to people and infrastructure residing in the northern and north western areas of Pakistan. This event triggered more than 100 aftershocks some of which were more than 6.5 Mw. Local site conditions
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