john's blog

According to Bath's law, a magnitude 9.0 earthquake shouild be followed by an aftershock of about 8.0  For the first week following the mainshock, there was no evidence of such an event.  However, the magnitude 6.8 aftershock that occurred about ahalf hour after the mainshock has now been upgraded to a 7.9 magnitude quake.  This event occurred about 100 km (60 miles) northwest of Tokyo. 

A colleague of mine flew from Los Angeles to Taipei, Taiwan yesterday to attend a scientific meeting.  Normally the flight path used by United airlines takes the aircraft down the eastern coast of Honshu, Japan, on its way to Taipei, or if it stops in Tokyo, to Narita.  On this trip the pilot gave an especially wide berth as the aircraft came abreast of Fukushima, passing within about 200 miles of the island. 

Here we update the forecast made for the four cities of Tokyo, Niigata, Osaka and Sendai.  The last update was the day after the M9.0 Great Tohoku earthquake.  Since March 13, the chance of an M6.7 within 12 months of March 17, 2011 and 150 miles of the four cities listed has increased for all cities as shown below.  Sendai is currently at highest risk, with Tokyo also at substantial risk.

In tabular form the data is:

These impressive simulations of the Japan earthquake tsunami were made by Dr. Steven Ward from UC Santa Cruz.  Dr Ward uses a variety of methods to produce these simulations. All of these movies show different versions of the same calculation.  The idea is that we can use simulations like these in a predictive sense.  Once we know something about the source, in this case an earthquake, we can then run a calculation to determine where the waves are likely to strike.

In the first movie, waves propagate across the Pacific basin, and run-up heights on the shore are estimated:

Visitors to this site have seen forecasts for the four California cites of Los Angeles, San Diego, San Francisco and Sacramento.  Some visitors have asked:  Has the Japanese M9.0 earthquake increased the seismic hazard in California?  As far as we can determine at this time, the answer is "no".