Abstract
In recent years, the Quetta Valley and surrounding areas have experienced unprecedented levels of subsidence, which has been attributed mainly to groundwater withdrawal. However, this region is also tectonically active and is home to several regional strike-slip faults, including the north–south striking left-lateral Chaman Fault System. Several large earthquakes have occurred recently in this area, including one deadly Mw 6.4 earthquake that struck on 28 October 2008. This study integrated Interferometric Synthetic Aperture Radar (InSAR) results with GPS, gravity, seismic reflection profiles, and earthquake centroid-moment-tensor (CMT) data to identify the impact of tectonic and anthropogenic processes on subsidence and earthquake patterns in this region. To detect and map the spatial-temporal features of the processes that led to the surface deformation, this study used two Synthetic Aperture Radar (SAR) time series, i.e., 15 Phased Array L-band Synthetic Aperture Radar (PALSAR) images acquired by an Advanced Land Observing Satellite (ALOS) from 2006–2011 and 40 Environmental Satellite (ENVISAT) Advanced Synthetic Aperture Radar (ASAR) images spanning 2003–2010. A Small Baseline Subset (SBAS) technique was used to investigate surface deformation. Five seismic lines totaling ~60 km, acquired in 2003, were used to map the blind thrust faults beneath a Quaternary alluvium layer. The median filtered SBAS-InSAR average velocity profile supports groundwater withdrawal as the dominant source of subsidence, with some contribution from tectonic subsidence in the Quetta Valley. Results of SBAS-InSAR multi-temporal analysis provide a better explanation for the pre-, co-, and post-seismic displacement pattern caused by the 2008 earthquake swarms across two strike-slip faults.
Highlights
The Quetta Valley is located in western Pakistan, in a 560 km-long and 150 km-wide complex belt of north–south-oriented mountain ranges and intervening valleys [1]
Subsidence in urban areas is generally attributed to groundwater depletion, it is not clear whether ground fissures in the Quetta Valley are caused by water withdrawal or related to the tectonics of the region
We attributed this movement primarily to uplift for the following reasons: (1) From the general tectonics of the area, the region is subject to thrust and north–south strike-slip faults, intervening valleys, and basins
Summary
The Quetta Valley is located in western Pakistan, in a 560 km-long and 150 km-wide complex belt of north–south-oriented mountain ranges and intervening valleys [1]. Four ground fissures appeared in February 2011 near the Quetta Valley that are oriented at ~25◦ and –25◦ to the north, with a ~6 m depth and ~2 m maximum width. Subsidence in urban areas is generally attributed to groundwater depletion, it is not clear whether ground fissures in the Quetta Valley are caused by water withdrawal or related to the tectonics of the region. The appearance of these fissures has prompted fears of earthquakes. Remote Sens. 2016, 8, 956; doi:10.3390/rs8110956 www.mdpi.com/journal/remotesensing
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