Complex faulting in the Quetta Syntaxis: fault source modeling of the October 28, 2008 earthquake sequence in Baluchistan, Pakistan, based on ALOS/PALSAR InSAR data

Abstract

The Quetta Syntaxis in western Baluchistan, Pakistan, is the result of an oroclinal bend of the western mountain belt and serves as a junction for different faults. As this area also lies close to the left-lateral strike-slip Chaman fault, which marks the boundary between the Indian and Eurasian plates, the resulting seismological behavior of this regime is very complex. In the region of the Quetta Syntaxis, close to the fold and thrust belt of the Sulaiman and Kirthar Ranges, an earthquake with a magnitude of 6.4 (Mw) occurred on October 28, 2008, which was followed by a doublet on the very next day. Six more shocks associated with these major events then occurred (one foreshock and five aftershocks), with moment magnitudes greater than 4. Numerous researchers have tried to explain the source of this sequence based on seismological, GPS, and Environmental Satellite (ENVISAT)/Advanced Synthetic Aperture Radar (ASAR) data. Here, we used Advanced Land Observing Satellite (ALOS)/Phased Array-type L-band Synthetic Aperture Radar (PALSAR) InSAR data sets from both ascending and descending orbits that allow us to more completely detect the deformation signals around the epicentral region. The results indicated that the shock sequence can be explained by two right-lateral and two left-lateral strike-slip faults that also included reverse slip. The right-lateral faults have a curved geometry. Moreover, whereas previous studies have explained the aftershock crustal deformation with a different fault source, we found that the same left-lateral segment of the conjugate fault was responsible for the aftershocks. We thus confirmed the complex surface deformation signals from the moderate-sized earthquake. Intra-plate crustal bending and shortening often seem to be accommodated as conjugate faulting, without any single preferred fault orientation. We also detected two possible landslide areas along with the crustal deformation pattern.

Fault source model for the 2016 Kumamoto earthquake sequence based on ALOS-2/PALSAR-2 pixel-offset data: evidence for dynamic slip partitioning

“…The fault surface is derived by spline interpolation, based on the given control points on the top and the bottom. The location and depth of the bottom of the faults, i.e., dip angle, were derived by trialand-error approach (Table 2; e.g., Furuya and Yasuda 2011;Abe et al 2013;Usman and Furuya 2015). Based on the given location and geometry of the fault, we can solve the slip distributions as a linear problem with the constraints noted below.…”

A study on the enhancing earthquake frequency in northern Pakistan: is the climate change responsible?

“…During the study of the October 28, 2008 shock sequence, in Baluchistan (Pakistan) based on the seismological and GPS data numerous researchers proposed that previously studied Urghaghai Fault as a possible source (Lisa and Jan 2010;Khan et al 2008;Yadav et al 2012). However, on the basis of synthetic aperture radar data, it became clear that a new complex geometry of conjugate faults was the responsible source (Pezzo et al 2014;Puyssegur et al 2014;Usman and Furuya 2015). In the intraplate compression regime, various parts of plates experience different style of deformation and exhibit corresponding strain partitioning of reverse, normal and strike slip faulting.…”

Coseismic Folding During Ramp Failure at the Front of the Sulaiman Fold‐and‐Thrust Belt

“…In the past hundred years, the frontal part of the eastern SFT has not experienced any earthquake of Mw > 6. In contrast, in the Western and Central SFT, several Mw 6.0–6.9 earthquakes occurred in the last decades, including a Mw 6.7 and 6.9 doublet in 1997 in the Sibi Syntaxis (Figure 5a) and Mw 6.4 events in 2008 in the Quetta Syntaxis (Figure 1a) (Nissen et al., 2016; Reynolds et al., 2015; Usman & Furuya, 2015). Ultimately, earthquakes accommodate fault slip and the frequency of earthquakes is linked to the long‐term fault slip‐rate.…”