Surface Rupture of the 2005 Kashmir, Pakistan, Earthquake and Its Active Tectonic Implications

Abstract

To provide a detailed record of a relatively rare thrust surface rupture and examine its active tectonic implications, we have conducted field mapping of the surface rupture associated with the 2005 M w 7.6 Kashmir earthquake. Despite the difficulty arising from massive earthquake-induced landslides along the surface rupture, we found that typical pressure ridges and warps extend northwestward for a distance of ∼70 km, with a northeast-side-up vertical separation of up to ∼7 m. Neither the main frontal thrust nor the main boundary thrust is responsible for the earthquake, but three active faults or fault segments within the Sub-Himalaya, collectively called the Balakot-Bagh fault, compose the causative fault. Although the fault exhibits substantial geomorphic expression of repeated similar surface ruptures, only a part of it had been mapped as active before the earthquake. The location of the hypocenter suggests that the rupture was initiated at a deep portion of the northern-central segment boundary and propagated bilaterally to eventually break all three segments. Our obtained surface rupture traces and the along-strike-slip distribution are both in good agreement with results of prompt analyses of satellite images, indicating that space geodesy can greatly aid in time-consuming field mapping of surface ruptures. Assuming that the extensive fill terrace in the meizoseismal area was abandoned during 10-30 ka, we tentatively estimate the earthquake recurrence interval and shortening rate on the Balakot-Bagh fault to be 1000-3300 yr and 1:4-4:1 mm=yr, respectively. These estimates indicate that the Balakot-Bagh fault is not a main player of Himalayan contraction accommodation. Ⓔ Selected field photographs and ArcGIS files of the mapped surface rupture traces and measured vertical separations are available in the electronic edition of BSSA.Online Material: Field photographs and ArcGIS files of surface rupture traces and vertical separations.

Proceedings of the 25th Himalaya-Karakoram-Tibet Workshop

“…Both the BB and RF are reverse faults; the BB locally cuts the 17 -12 Ma Kamlial Formation. A balanced cross-section indicates a minimum of 20 km fault displacement on the BB, yielding a minimum 1.2-1.7 mm/yr long-term slip rate, lower than the 1.4 -4.1 mm/yr slip rate inferred from faulted Quaternary fluvial terraces (Kaneda, 2008). The penultimate earthquake occurred between 500 and 2200 yr b.p.…”

“…A seismically active emergent thrust fault system extends stepwise from the Balakot-Bagh fault (BB; source of the Mw=7.6, 2005 Kashmir earthquake (Kaneda, 2008;Kumahara and Nakata, 2006)) southeast more than 200 km to the Reasi fault (RF) (Hussain and others, 2009). Both the BB and RF are reverse faults; the BB locally cuts the 17 -12 Ma Kamlial Formation.…”

Width of surface rupture zone for thrust earthquakes: implications for earthquake fault zoning

“…In particular, B-M fault ruptures, which are related to the presence of large-scale hanging wall anticlines, were clearly observed in the El Asnam 1980 (Philip and Meghraoui, 1983) and Kashmir 2005 (southern part of central segment; Kaneda et al, 2008;Sayab and Khan, 2010) earthquakes. A wide extensional zone (1.8 km long in the E-W direction; 1.3 km wide) formed on the eastern hanging wall side of the Sylmar segment of the San Fernando 1971 surface rupture.…”

Geostatistical and space geodetic methods on a 3D coseismic displacement field

“…Due to Rapid discharge flow of rivers, erosion rate is high, which produces steep lower valley slopes. Muzaffarabad, about 10 km south west of the epicenter, is the largest city in the region, with a population of about 200,000 and was severely damaged during the 2005 Kashmir earthquake (Naeem et al, 2005;Kaneda et al, 2008;Hussain et al, 2009). …”

“…fault mechanics and geometry), future earthquake recurrence and seismic hazard assessment (Leprince et al, 2007;Kaneda et al, 2008). Moreover, these measurements also assist in interpretation of morphotectonic features in other earthquake prone areas for preparing seismic hazard maps (Binet and Bollinger, 2005;Kaneda et al, 2008).…”