Earthquake swarms continued Wednesday in Imperial County as the city of Brawley declared an emergency to deal with the damage.

The swarm that began Sunday morning showed signs of slowing down Wednesday, with fewer quakes reported by the U.S. Geological Survey than on recent days. The magnitude of the quakes is also declining.

There was scattered damage around Brawley, but officials have not yet compiled a full estimate of the costs. The Brawley City Council on Tuesday declared a local emergency, according to the Imperial Valley Press.

More than 400 earthquakes greater than magnitude 1.0 have been recorded in Imperial County since Saturday evening, said U.S. Geological Survey geophysicist Elizabeth Cochran. The largest were a 5.3 and a 5.5 about midday Sunday.

Scientists say the reason is not fully understood, but there is a clue: Earthquake faults work much differently south of the Salton Sea than they do closer to Los Angeles.

Take, for instance, the San Andreas fault as it runs through Los Angeles County. It’s a fault where, generally speaking, two plates of the Earth’s crust are grinding past each other. The Pacific plate is moving to the northwest, while the North American plate is pushing to the southeast.

South of the Salton Sea, the fault dynamic changes. The Pacific and North American plates start to pull away from each other, Cochran told The Times from her Pasadena office. (Tha.