The 2013 Mw 7.7 Balochistan Earthquake: Seismic Potential of an Accretionary Wedge

Abstract

Great earthquakes rarely occur within active accretionary prisms, despite the intense long-term deformation associated with the formation of these geologic structures. This paucity of earthquakes is often attributed to partitioning of deformation across multiple structures as well as aseismic deformation within and at the base of the prism (Davis et al., 1983). We use teleseismic data and satellite optical and radar imaging of the 2013 M w 7.7 earthquake that occurred on the southeastern edge of the Makran plate boundary zone to study this unexpected earthquake. We first compute a multiple point-source solution from W-phase waveforms to estimate fault geometry and rupture duration and timing. We then derive the distribution of subsurface fault slip from geodetic coseismic offsets. We sample for the slip posterior probability density function using a Bayesian approach, including a full description of the data covariance and accounting for errors in the elastic structure of the crust. The rupture nucleated on a subvertical segment, branching out of the Chaman fault system, and grew into a major earthquake along a 50°north-dipping thrust fault with significant along-strike curvature. Fault slip propagated at an average speed of 3:0 km=s for about 180 km and is concentrated in the top 10 km with no displacement on the underlying décollement. This earthquake does not exhibit significant slip deficit near the surface, nor is there significant segmentation of the rupture. We propose that complex interaction between the subduction accommodating the Arabia-Eurasia convergence to the south and the Ornach Nal fault plate boundary between India and Eurasia resulted in the significant strain gradient observed prior to this earthquake. Convergence in this region is accommodated both along the subduction megathrust and as internal deformation of the accretionary wedge.

An Investigation of 2013 M_w 7.7 Awaran Earthquake, Pakistan

“…Makran mega thrust was ruptured by a M w 8.0 earthquake in 1945. Chaman fault system is a 1200 Km long, left-lateral fault system accommodating 3cm/yr northward motion of India with respect to Eurasia [8]. It extends south towards the subduction zone through Ghazaband and Ornach Nal fault systems [9,10].…”

“…In addition, immense variation in the non-double component was revealed from different earthquake focal mechanisms (W-Phase, surface wave and body-wave solution). This suggests a significant source complexity [8]. Satellite studies suggest active thrusting accretionary prism including the Hoshab fault [19].…”

“…According to Jolivet et al 2014 [8], the 2013 rupture was majorly left-lateral strike slip and involves a minor oblique reverse motion. The majority of slip occurred at shallow depths of < ~ 10 Km.…”

Spatio-Temporal Error Sources Analysis and Accuracy Improvement in Landsat 8 Image Ground Displacement Measurements

“…In addition, a Mw 7.7 earthquake happened there on 23 September 2013, leaving obvious surface ruptures [25,[27][28][29]. Totally, 25 images covering the study area (Path: 154, Row: 42, see Figure 1, Table A1) are selected, pairing freely with a temporal baseline of 16 days (see Figure A1) and calculating mutually image deformation fields.…”

“…Since its operation, the Landsat 8 data have been applied to monitor earth surface movements. Many studies demonstrate that the Landsat 8 image cross-correlation technique has advantages in measuring surface deformation, such as mapping ice sheet velocity [26], coseismic deformation extraction [25,[27][28][29] and volcano deformation monitoring [30]. Many researchers have done a lot of analyses and error source correction of displacement measurement, but they mainly focused on a few data sources, such as SPOT, ASTER, HiRISE (High Resolution Imaging Science Experiment) and aerial imagery [3,8,11,[13][14][15][16][17][19][20][21]31,32].…”