As you all know by now, a 7.2 magnitude earthquake struck along the Mexican/California border yesterday, severely damaging some structures in Mexico but causing only minor disruptions — and a big scare — for those in Southern California, despite being the biggest shock to hit the area in two decades. According to risk modeling company EQECAT, most of the economic damage occurred in Mexico (Mexicali, specifically) and overall losses will not exceed $1 billion, with insured losses totaling $300 million.
Although damage will have occurred in both Mexico and the US, the community of Mexicali is the largest urban area affected by this event, and damage there is expected to be widespread. The largest US city affected by the earthquake is El Centro, California, although significantly less damage is expected there than in Mexicali, due both to lower-intensity ground shaking and less-vulnerable structures.
Structures with greater earthquake resistance may have experienced slight to moderate damage. The intensity of shaking that occurred in El Centro and other US locations is below the threshold typically associated with structural damage.
This earthquake ruptured on the Laguna Salada fault, whose last major earthquake occurred in 1892, to the northwest of yesterday’s rupture. Another historic earthquake that affected the region was the 1940 Imperial Valley (US) earthquake (M6.9), which caused strong shaking in the US cities of El Centro and Brawley. Buildings damaged in 1940 will have been repaired or replaced, and highly-vulnerable buildings were not reconstructed in the El Centro region.
However, border cities such as Mexicali had not experienced shaking as severe as from yesterday’s quake for nearly 100 years. Consequently, many buildings in Mexicali will have been at risk to major damage, particularly older commercial and residential structures, and particularly those built of unreinforced masonry. Unreinforced masonry buildings have consistently demonstrated vulnerability to damage from earthquakes.
Let’s hope any after shocks do minimal harm.
ABC also offers the following video report.