Earthquake activity remains at 'elevated level' amid more aftershocks, USGS says
The California-Mexico border continued to rattled by what the U.S. Geological Survey called an "elevated level" of earthquake activity as hundreds of aftershocks to Monday's 5.7 temblor were recorded.
Monday's quake was itself an aftershock of the 7.2 magnitude Easter Sunday quake that hit the Mexicali area, causing two deaths. There was more than $90 million in damage in California alone.
In a summary posted on its website, the USGS described Monday's quake "the largest [aftershock] so far of the M7.2 [quake]. This aftershock was located within the large cluster of aftershocks at the northwest end of the ongoing aftershock sequence. The M5.7 event was followed by its own vigorous aftershock sequence."
The USGS also said the 5.7 quake "probably occurred on a northwest striking fault that follows the trend of the Elsinore fault in this region. The Elsinore fault is more than 110 miles long, and extends into the Orange County and Los Angeles area as the Whittier fault."
Experts have said the 7.2 temblor has caused thousands of aftershocks, increasing overall seismic activity in the Southern California-Baja California region.
There were dozens of aftershocks overnight, but fewer were greater than 3.0 magnitude when compared to Tuesday or Wednesday.
On Thursday morning, a 4.1-magnitude quake on the border was reported; it probably was an aftershock of the April quake.
-- Shelby Grad
Map: Map of historic earthquake cycles in border region. Credit: USGS