Teleseisms

(A teleseism is a record of an earthquake made by a seismograph at a great distance.)

On April 23, 2000, a magnitude 6.9 (Mw) earthquake occurred at 09:27:23.1 (UTC*) approximately 600 km below Santiago del Estero Province, Argentina (1). The fastest-traveling seismic waves (P-waves) traveled through the earth's mantle and arrived at station PMM (located near Parkfield, California) about 11 minutes later, at 09:38:55 UTC (2). The slower-traveling S-waves also travelled through the mantle, and reached Parkfield 21 minutes after the earthquake occurred (3). The signal arriving at 08:49 (green trace) is from a M=3.4 earthquake (origin time 08:48:39) in southern California, approximately 200 km ESE of this station. The signal at 10:07 (black trace) is a (yet unidentified) later arrival from the Argentina event.

A second earthquake under Argentina, magnitude 7.0 (Mw), occurred May 12, 2000, at 18:43:20.2 (UTC), 240 km below Jujuy Province. The record from this earthquake again at station PMM, is similar to that from the April 23rd event because the events occurred in roughly the same area and are both relatively deep.

* UTC is Universal Time, also known as Greenwich Mean Time.