Magnitude 7.8-7.9 earthquake strikes near Katmandu, Nepal

Location of earthquake and initial aftershocks
From CNN.com

Added on 4/29: Here is a link to an Andrew Revkin article in the New York Times with excellent information about why Max Wyss thinks that the death toll could reach 57,700, and the range of uncertainty. 

Map added on 4/26 at bottom showing avalanche problems on Mount Everest.

A 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 text

The 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.com

A 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.

The situation on Mount Everest as
shown in NYTimes.com

News is trickling in that devastating avalanches have killed approximately 20 people on Mount Everest. Sadly, the best time to climb Mount Everest from a weather perspective is now, April and May. Sadly, on April 18, 2014, thirteen people were killed in an avalanche, at a site well known for its danger.  There is a dangerous ice fall, known as the Khumbu Icefall, where seracs (unstable blocks of ice separated by cracks in an ice field) loom large over the route.  Climbers usually try to pass quickly through here in the early morning before rising day temperatures amplify the hazard.  According to Wiki, citing Russell Brice who runs a guide company called Himalayan Experience, ice falling from the serac narrowly missed climbers in 2012, and according to another mountaineer/writer, Jon Krakauer, the 2014 avalanche was triggered when a large block of ice broke off from the bulge. The Khumbu Icefall and the location of the 2014 avalanche are shown on the adjacent figure. It will be very interesting to see if the present large avalanche originated at the same site, but travelled much further all the way down the ice fall to cause so much damage in the Base Camp.

Remember that Nepal is landlocked. Tom Robinson of the University of Canterbury has done a preliminary analysis of the roads likely to be affected by landslides; that analysis is available on Dave's Landslide Blog here. The rescue situation w is dreadfully complicated with the airport closed and most access roads damaged by landslides. (Correction: The airport is open and India and China are flying in relief.) The monsoons are less than two months away, and since it is likely that many rivers are blocked by landslides, air and satellite photography of the landslide settings is essential to analyze future flooding due to blocked rivers.