Given the recent Beverly Hills quake and the accompanying microseismicity, I thought
it might be worthwhile to resurrect this post which was posted on September 10 the
day before the world changed (#9400 in archives):

Thoughts on the Hollywood earthquake from a local seismologist
Posted by Lowell on September 10, 2001 at 15:54:44:

Received the following e-mail today. Thought the board might be interested to
see what is being discussed in Pasadena regarding the Hollywood earthquake.

Date: Sun, 9 Sep 2001 20:36:29 -0700 (PDT)
From: Egill Hauksson
To: kate@gps.caltech.edu
Mime-Version: 1.0

M4.2 Earthquake Occurs in West Hollywood, City of Los Angeles

Egill Hauksson and Kate Hutton, Caltech,
Lucy Jones, USGS

See also www.trinet.org

A M4.2 earthquake occurred in West Hollywood, City of Los Angeles California at
4:59 pm (local time) September 9, 2001. This earthquake was widely felt
throughout the Los Angeles Basin and in parts of San Fernando Valley and was
well recorded by the Caltech-USGS TriNet. The focal depth of this earthquake
was about 4 km, making the shaking most severe in the Hollywood basin. No
significant damage has been reported.

During the last two weeks a north-northwest trending cluster of seismicity
preceded the M4.2 earthquake. This cluster crossed the epicentral area of the
M4.2 extended from Inglewood in the south, to Northridge in the north. These
quakes had magnitudes in the range from M1.3 to M2.0.

This earthquake is located near the intersection of the Newport-Inglewood and
Hollywood faults. The focal mechanism showed horizontal strike-slip motion on a
north-northwest striking plane, suggesting that this event may be associated
with the north end of the Newport-Inglewood fault.

The Los Angles basin has north-northwest trending strike-slip faults at shallow
depth and east-west trending thrust faults at depths greater than 6 to 8 miles.
This earthquake differs from of the deep thrust faulting earthquake sequences
recorded over the last two decades in the Los Angeles area such as 1987 M5.9
Whittier Narrows and 1994 M6.7 Northridge. The occurrence of this earthquake
cluster suggest activation of the more shallow strike-slip regime of fault s in
the Los Angeles basin, which has mostly remained dormant over the last decade.