posted Jul 30, 2012, 6:27 AM by Weather Man
[
updated Jul 30, 2012, 6:40 AM
]
M6.0 - 26km SW of Ocos, Guatemala 2012-07-29 12:22:15 UTC - On 29. July 2012 12:22:15 PM, an earthquake occurred in Guatemala
potentially affecting 2020000 people within 100km. The earthquake had
magnitude 6M and depth 35.5km.
and
M4.4 - 25km SSE of Santiago Jamiltepec, Mexico 2012-07-29 23:10:31 UTC

Seismotectonics of Mexico
Located atop three of the large tectonic plates, Mexico is one of
the world's most seismologically active regions. The relative motion
of these crustal plates causes frequent earthquakes and occasional
volcanic eruptions. Most of the Mexican landmass is on the westward
moving North American plate. The Pacific Ocean floor south of Mexico
is being carried northeastward by the underlying Cocos plate. Because
oceanic crust is relatively dense, when the Pacific Ocean floor
encounters the lighter continental crust of the Mexican landmass, the
ocean floor is subducted beneath the North American plate creating the
deep Middle American trench along Mexico's southern coast. Also as a
result of this convergence, the westward moving Mexico landmass is
slowed and crumpled creating the mountain ranges of southern Mexico
and earthquakes near Mexico's southern coast. As the oceanic crust is
pulled downward, it melts; the molten material is then forced upward
through weaknesses in the overlying continental crust. This process
has created a region of volcanoes across south-central Mexico known as
the Cordillera Neovolcánica.
The area west of the Gulf of
California, including Mexico's Baja California Peninsula, is moving
northwestward with the Pacific plate at about 95 mm per year. Here,
the Pacific and North American plates grind past each other creating
strike-slip faulting, the southern extension of California's San
Andreas fault. In the past, this relative plate motion pulled Baja
California away from the coast forming the Gulf of California and is
the cause of earthquakes in the Gulf of California region today.
Mexico has a long history of destructive earthquakes and volcanic
eruptions. In September 1985, a magnitude 8.1 earthquake killed more
than 9,500 people in Mexico City. In southern Mexico, Volcán de Colima
and El Chichón erupted in 2005 and 1982, respectively. Paricutín
volcano, west of Mexico City, began venting smoke in a cornfield in
1943; a decade later this new volcano had grown to a height of 424
meters. Popocatépetl and Ixtaccíhuatl volcanos ("smoking mountain" and
"white lady", respectively), southeast of Mexico City, occasionally
vent gas that can be clearly seen from the City, a reminder that
volcanic activity is ongoing. In 1994 and 2000 Popocatépetl renewed
its activity forcing the evacuation of nearby towns, causing
seismologists and government officials to be concerned about the effect a
large-scale eruption might have on the heavily populated region.
Popocatépetl volcano last erupted in 2010.
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