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Magnitude 7.8-7.9 earthquake strikes near Katmandu, Nepal

Location of earthquake and initial aftershocks
From CNN.comA strong earthquake occurred in Nepal about 14 hours ago, and as I write this the death toll from the earthquake has risen to 1,457, with more deaths expected. The people face a cold night without shelter, water or electricity in many regions. The world's thoughts are focused on the people of Nepal with hopes that rescue efforts proceed smoothly an rapidly.

Max Wyss, Switzerland, runs a research program WAPMERR, in which he combines geographic data with seismic models to predict the injured and dead, with results sent to authorities and emergency people to aid in the planning of rescue and recovery (Note: you can subscribe to his service on the home page of WAPMERR). Unfortunately, his estimates are for 2000-10,000 fatalities, and 20,000-70,000 injuries. (Wyss's estimates have been updated to the numbers that I cite here just in the time it has taken to write this post, so check back with his site if you want updated information.)

According to the USGS, large earthquakes in this region have been relatively rare with only four events of M6 or larger known to have occurred within 250 km of this earthquake site. Two of these were a M6.9 earthquake in 1988, that caused about 1500 casualties and a M8.0 event in 1934 at roughly the same location of this 1988 event that severely damaged Katmandu and caused around 10,600 casualties.

Image from Dave's Landslide Blog showing the
location of the earthquake according to USGS model
Image from Blog as cited in the textThe earthquake struck near noon local time (11:56 a.m.), 11:11 p.m. the previous day, west coast time in the U.S. A magnitude 6.6 aftershock occurred about a half hour later, and strong aftershocks continue. It was centered less than 50 miles west of Katmandu, with aftershocks surrounding the capital on the north and east (see map). Katmandu sits in a valley of 1,000,000 people. There are reports that roads buckled in Tibet, and that avalanches were triggered on Mount Everest. The magnitude of the earthquake has been reported from M7.5-M7.9, and the epicenter at 7-12 km. These estimates should get better as seismologists have time to refine the models and analyze the data, but it is clear that the quake was quite shallow.

The Indian and Eurasian plates are converging at a rate of 45 mm/year, one of the fastest rates on the planet. This motion drives the uplift of the Himalayas. India is thrust under Eurasia, and the motion between the two plates makes this one of the seismically most hazardous regions in the world. The surface expression of the fault (along the red line in the figure below) in the vicinity of Nepal is marked by the east-west trending Himalaya Front in the north of India and Nepal sits within this belt. To the north is the high Plateau of Tibet. An excellent detailed summary of the regional tectonic setting is available on the USGS events page reporting the current earthquake found here.

The tectonic boundary between the Indian plate (bottom)
and Eurasian plate (top) with the red line showing
the surface location of the collision of these
two plates. USGS map as published today in USAToday.comA 2004 thesis by Bierendra Kumar Piya concluded that there was a significant potential for liquefaction in the Katmandu valley in the case of a strong earthquake. He noted that liquefaction occurred in parts of the valley in the 1934 earthquake, which this one closely resembles, so we expect to see reports of damage to buildings and infrastructure due to liquefaction. There is also a strong possibility of landslides. Dave's Landslide Blog at AGU (starting on April 25, 2015) will be updating and discussing the landslides.

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