Lahore, Pakistan: An earthquake jolted in Pakistan. It has been observed that the Magnitude is expected at 4.3, but authorities are yet to announce it officially. Earquake jolted several parts of the country, including Lahore, Islamabad, Peshawar, Multan, and nearby areas. Reports are circulating that people came out of their tall offices immediately after the tremors were felt.
According research conducted by Mona Lisa and M. Qasim Jan titled “August 08, 2010, Sheikhupura, Pakistan earthquake: a seismotectonic investigation using focal mechanism solution and gravity data”, indicates a shallow-focus (3.8 km deep) and low-magnitude (ML 3.8) earthquake occurred near Sheikhupura on August 08, 2010. January 4, 2023 earthquake came from the same spot therefore following information provided by Mona Lisa and Qasim Jan in their research is very important to share here.
Tectonically, this earthquake occurred to the south of the Salt Range in the Punjab Seismic Zone (PSZ), a shallow-focus, moderate-level seismic zone characterized by steeply dipping strike-slip and extensional faults. The United States Geological Survey and local observatory, shows an EW-trending fault plane dipping 710 N similar to the normal faults reported in the area previously. On the basis of the imposition of the stress field on the northward-moving Indian plate and the nature of the FMS of the previous and this earthquake, the Sheikhupura earthquake is considered as one of the intraplate earthquakes occurring frequently in the PSZ. The location of the event on the Bouguer gravity maps coincides with the zone of high gravity anomaly reflecting igneous intrusion(s) or, more likely, structural disturbances (i.e., extensional faulting in the basement.
The earthquake occurred in a zone called the Punjab Seismic Zone (PSZ) that stretches from the eastern flank of the Sulaiman Range through northern Punjab to Lahore and beyond (Seeber and Armbruster 1979). Because of the proximity of the large urban centers, seismicity in the PSZ, including the Sheikhupura event, requires careful studies. The basement is seismically active and characterized by shallow-focus, moderate-level earthquakes caused due to steeply dipping strike-slip and extensional faults (Kazmi and Jan 1997) in the PSZ. No prominent surface structures have been reported by previous workers in this part of the Punjab plain, except an EW-trending normal fault, only 25 km south of the Sheikhupura earthquake epicenter, in the PSZ. Some 160 km WNW in the Salt Range, however, NW-trending strike-slip faults have been reported by Seeber and Armbruster (1979) and other workers.
The northern Punjab plain is tectonically located to the south of the Salt Range. The PSZ of relatively high seismicity corresponds to a zone of high gravity (Duroy et al. 1989; Kadri 1995). From gravity data and mapping of isolated outcrops in the region, it has been assumed that the alluvial plain is underlain by a Precambrian basement [see Kazmi and Jan (1997) for review]. From Bouguer anomaly data, Farah et al. (1977) suggested that the Sargodha basement high underthrusts the front of the Salt Range in the west. According to Seeber and Armbruster (1979), seismicity in northern Pakistan occurs over a large crustal depth range, with maximum depth increasing gradually from 35 km in the area where the Precambrian rocks of the Indian shield outcrop in the Punjab plains to 70 km under the Higher Himalayas. New tectonic uplifts south of the Salt Range Thrust and Himalayan Front Thrust represent an outward step of the plate boundary from the principal tectonic displacement zone into the Punjab Plain (Yeats and Thakur 2008). Based on the analysis of 81 events (1990–1994) of Indian Meteorological Department’s local observatory data, Verma et al. (1995) showed that the intraplate seismicity in the area results from northward movement of the Indian plate. Recent seismological data from local observatories in northern Pakistan indicate the activation of shallow-level upper crustal faults (MonaLisa et al. 2007, 2008; MonaLisa 2009). The location of the Sheikhupura earthquake on the Bouguer gravity anomaly map coincides with the zone of high gravity, reflecting igneous intrusion(s) or structural disturbances, that is, basement normal faulting. The regional Bouguer anomaly data of the Punjab Plain by Farah et al. (1977) show a horst-like block of raised continental crust extending northwestward with gentle dips.
