By David Jacobson, Temblor
At just past 3 a.m. local time on February 8, a M=6.3 earthquake shook southern Pakistan, near the city of Pasni, which is home to approximately 33,000 people. Because of the remoteness of this location, and the political climate of the region, information is slow to come in. However, at this stage, we know that some buildings have collapsed, and that so far, there are no reports of fatalities. Some building damage is not surprising as many structures are made of stone masonry and block construction. The USGS estimates that fatalities are unlikely, and that damage should remain limited.
Within this portion of Pakistan, compression is the main tectonic force. The Makran Trench lies just 100 km off the southern coast, and is where the Arabian plate subducts beneath the continental Eurasia plate. This compression is what formed the Zagros Mountains, which stretch for over 1,500 km from Turkey through Iran.
Even though subduction is slow here, the area has experienced large earthquakes. On November 27, 1945, a M=8.0 earthquake shook the region, in the process, generating a tsunami within both the Gulf of Oman and the Arabian Sea. The shaking and ensuing tsunami from this mega-thrust event killed an estimated 4,000 people. This deadly event occurred approximately 85 km southwest of today’s M=6.3 quake, which also appears to have occurred along or near the subduction zone.
So far, there has only been one large aftershock from today’s M=6.3 event. The aftershock, a M=5.2 occurred approximately 13 hours after the mainshock. Based on the Global Earthquake Activity Rate (GEAR) model, which is available in Temblor, today’s M=6.3 cannot be surprising. GEAR is a global model, which uses global strain rates derived from GPS velocities and M≥5.8 quakes since 1977 to forecast future events. Based on this model, a M=6.0-6.25 earthquake is likely in your lifetime in this region in Pakistan, which is almost exactly what the magnitude was. Should any more information come in on this earthquake, we will be sure to update this post.