Saturday, July 12, 2014

Biggest aftershock yet from Duncan quake - M 4.1

A magnitude 4.1 aftershock last night at 7:48 p.m. local time, is the biggest since the main 5.2 Duncan earthquake struck on June 28.  [Right, southern-most orange circle is the M 4.1 event.  Credit, USGS]

There was another M 3.0 aftershock at 12:53 a.m. this morning.  That makes 7 events in a day and half of about magnitude 3 or larger, most of which were felt by local residents and some at least 30 miles away.


  1. Are earthquakes just a part of daily life now for Arizona citizens, or would you predict a major earthquake in the next decade and these tremors are signals?

  2. Scientists have yet to successfully predict earthquakes but we can provide forecasts in general of how big an earthquake we can expect in an area over a period of time, by analyzing the earthquakes and aftershocks that occur. We are still collecting the data on the Duncan earthquake and cannot yet say anything about whether this may increase or decrease the likelihood of other earthquakes in the future.

    There was a similar earthquake with comparable aftershocks in the general area in 1938. We are not able to say if we should expect another in 75 years. There was a M 7.2 earthquake across the border in Mexico in 1887 that caused widespread damage. Studies of the fault rupture indicate a similar earthquake might only be expected every 1,000 - 2,000 years, on that fault system. However, there may be other fault systems, known or unknown, that could rupture on their own timeline

    These earthquakes are helping to better model the seismic environment. We have a long way to go to understand it as well as it is in California. Could we have a major quake in the next decade? Yes. Are the aftershocks a signal that one is coming? We have not seen any evidence that this is the case.