The thread on "Realism on a California Earthquake" got me thinking about a comparison with the recent actual quake in Nepal.

Size of Quake

The Nepal quake of April 25, 2015 was a M 7.8, and was followed a day later with a M 6.7 aftershock.

This is roughly comparable to what might be expected for the "big one" on the southern San Andreas Fault. Indeed, the hypothetical earthquake the USGS envisioned for the ShakeOut Scenario was also an M 7.8.

Population Involved

Nepal's population is about 28 million. I can't find the reference at the moment, but I recall reading that the UN said about 6 million people were directly impacted by the Nepal quake.

Pete's estimate in the other thread was that there are about 13 million people in SoCal, and he assumed about half , or about 6.5 million people might be directly impacted. Recognizing that both these estimates are very approximate at best, it is clear that roughly comparable numbers of people might be directly effected.

Infrastructure and Preparedness

Nepal is a developing country, that until recently was in the midst of a civil war. The government was barely functional in the best of times. While some efforts had been made to prepare for earthquakes, most of the construction was not seismic resistant. Nepal is also a very rugged country, with few modern roads. Much of the country is only accessible by foot, even in normal times. There is only one modern airport at Kathmandu capable of landing large aircraft.

California is overall a very modern state. Recent building codes take earthquakes into account. While by no means all older structures have been seismically retrofitted, many have. In recent years CalTrans has made major efforts to retrofit existing bridges and other highway structures. While some areas in California are topographically rugged, most populated areas are nowhere near as difficult terrain as is Nepal. California has an excellent modern highway system and numerous fine airports.

Earthquake Casualties

The 2015 Nepal quake killed about 8,800 people and badly injured more than 23,000. Hundreds of thousands were made homeless, just prior to the start of the monsoon in June.

We don't know how many would die in SoCal, since the "big one" hasn't happened yet. The ShakeOut Scenario (page 201) estimated 1,800 deaths, 750 major injuries, and more than 50,000 minor injuries.

Emergency Response and Recovery

In spite of a rapid and world wide response, the effort in Nepal has been severely handicapped by the rugged terrain and minimal infrastructure. The fact that even in normal times the Kathmandu Valley has only one reliable road to India, and only one airport capable of handling large aircraft has made post earthquake support from outside very challenging. Much of the country is inaccessible except by foot or helicopter.

Even allowing for major disruptions due to earthquake damage, it would appear that SoCal would face a much less severe problem for getting help from the outside world. While terminals and hangers may be demolished, airstrips themselves generally don't get too severely damaged in earthquakes. And California has an abundance of fine airstrips. Likewise, while roads may be damaged, a bit of work with a D-9 Cat can quickly make a damaged road passable, at least for emergency convoys.

None of the above is to say that a major earthquake in Southern California wouldn't be a severe disaster. Many people would die. And it would be a long time before things returned to normal. But I think all things considered, California is much better prepared than Nepal was.