Q: Do shallow or deep earthquakes have more aftershocks?
A: The 4.3 earthquake that struck Cle Elum early this morning had its focus less than four miles deep, and for an earthquake, that's very shallow.
But what does the depth of an earthquake really mean to us living on the surface?
Shallow-focus earthquakes are generally less than 40 miles deep with strong shaking near the epicenter – the point in the earth where the rupture occurs. Deep-focus earthquakes are greater than 40 miles deep with shaking felt over a wider area.
The Nisqually Earthquake in 2001 that shook Seattle (with an epicenter in Pierce County) was an exception. That was shallow-focus earthquake that was felt over a wide area.
Shallow-focus earthquakes often produce a lot of aftershocks, or they can if the initial earthquake is a significant magnitude. Deep focus earthquakes typically don’t produce as many aftershocks.
The quake at 1:04 a.m. Wednesday was centered about 20 miles north of Ellensburg and 10 miles northeast of Cle Elum in central Washington. Dispatchers for the Kittitas County sheriff's office say they received calls from people who felt it but did not report any damage.
The U.S. Geological Survey website showed more than 150 reports of the quake being felt throughout a wide area of central Washington. There were reports from Pasco to Puyallup.
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