TROPICAL STORM ARLENE MAY TRIGGER SEISMICITY IN MEXICO
Posted by JAC on 7/1/2011, 7:30 am
http://www.earthquakesummary.info/

EARTHQUAKE SUMMARY FOR JUNE 29, 2011

Tropical Storm Arlene will make landfall on the Vera Cruz area of eastern Mexico in the next day. This is the first storm of the Hurricane Season. Such hurricanes are often associated with increased seismicity as the stress patterns near the top of the tectonic plate are changed due to the low pressure associated with the storm. TS Arlene continued on the eastern coast of Mexico today with gusts up to 65 kts. Arlene is expected to move directly westward into inland central Mexico over the next two days. Hurricane and Tropical Storm watches are  in effect for the coast from La Pesca to Veracruz, Mexico. The storm is expected to pass directly over Queretaro, Mexico where an M 4.2, the first in many years occurred on June 25. Because of the low pressures over land associated and the fact that this is the first tropical storm of the new season in Mexico we expect the seismicity in Central and eastern Mexico especially in Oaxaca, Chiapas and Guerrero to be increased by up to 20% in expected magnitude. A large earthquake could occur in the Mexican subduction zone in the next week as such events are often associated with the first tropical storm of the season. We estimate the possibility of an event in this area of M>=6.5 at 20% and at M>=7.0 at 10% during this period.

This appears to be a repeat of the situation at this time last year. On June 30, Hurricane Alex was bearing down on the same area of Mexico. Seismicity associated with this hurricane included an M 6.2 in Oaxaca, the strongest earthquake in Mexico between April 2010 and April 2011. On July 1, 2011 we reported on this event in this summary as follows and the same applies today:

"This earthquake (Alex) hit while Hurricane Alex was located over the subduction zone to the north. This lowered the pressure over the upper subduction zone allowing it to rise with respected to the lower subduction zone. This separation between the two portions of the plate is likely a triggering effect behind today's earthquake." (July 1, 2010)

The other large regional event in the past three years, an M 6.6 in Chiapas, Mexico was also associated with a similar hurricane which was located north of Chiapas at the time of that earthquake on October 15, 2008.

The only other strong earthquake in Mexico in the past three years occurred in Jalisco on September 24, 2009 with M 6.4. It was associated with  Hurricane Marty passing to the south at the time of this event.

In both cases we had issued a seismic warning based on the positioning of these hurricanes. For example several days before the September 2009 event we noted here:

"Marty ... is a major storm and seismicity ... may increase, possibly as high as events of M>=5 in the region during the next week" (Sept. 16-20, 2009)

and in October, 2008 we noted:

"An unusual series of storms have hit this region in the past week. These included Tropical Storm Odile which passed through the region in teh past two days and  a second storm which passed over northern Chiapas last week. We had at the time noted these disturbances and suggested they may trigger a strong quake in the Chiapas area." (October 16, 2008)                                      

Current seismicity in Mexico is concentrated in the region northeast of Petatlan, Guerrero and in the Chiapas region. Any major event in the area at this time is likely to be near one of these two epicentral regions.



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Arlene Is Here! - CX, 6/28/2011, 7:25 pm
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