According to a new study, a fault previously considered as dormant may cause a Mw 6.4 earthquake in the region of Los Angeles.
The Wilmington blind‐thrust fault is located deep beneath the LA area. In particular, its length is about 18 kilometers and runs Northwest to Southeast under the LA basin.
The existence of the fault is widely-known since the 1930s but it was not considered hazardous as it was thought to be inactive since the Pliocene era. Wilmington fault has been thoroughly studied since it lies beneath the Wilmington Oil Field. Research, back then, revealed the existence of the fault as folding appeared in the subsurface's deep layers. Nevertheless, folding did not extend to the shallower layers of rock and, therefore, the study concluded that the fault has been dormant.
However, about a decade ago, a United States Geological Survey (USGS) scientist disputed this statement. It was found that some folding also appears in the shallow layers of the rock formations.
Now, the current research confirms that the situation is different. "We define the Wilmington blind‐thrust as a tectonically active fault capable of generating large damaging earthquakes...This overturns the long‐held view that the fault became dormant in the Late Pliocene, barring its inclusion in state‐of‐the‐art regional earthquake hazard assessments," the study suggests.
The potential tremblor would affect the ports of LA and Long Beach and the broader LA metropolitan area. “It doesn’t rupture frequently, but it’s like a sleeping giant beneath the harbor. Just because it’s slow, doesn’t mean it’s not dangerous," Franklin Wolfe, lead author of the study and doctoral student at Department of Earth and Planetary Sciences, Harvard University, stated. Moreover, if the fault is connected with other faults, a larger seismic shock (Mw>7.0) could be generated.
Wolfe raises the question of whether more faults that are not considered hazardous could produce devastating earthquakes in LA. “It makes you wonder how many other faults are in California that are not detected and slow moving. The San Andreas fault is the most noteworthy, but many other of faults in California capable of generating damage,” Wolfe stated.
Sources: SFgate, Washingtonpost, LAtimes
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