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Re: 7.0 Landers Aftershock

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Greg Smith wrote:

>      Why is this being called an aftershock?  It seems that an earthquake
> has occured.  Hope everyone's OK.
>
> Greg
>
> -----Original Message-----
> From: Roger Turk <73527.1356(--nospam--at)compuserve.com>
> To: seaint(--nospam--at)seaint.org <seaint(--nospam--at)seaint.org>
> Date: Saturday, October 16, 1999 1:34 PM
> Subject: RE: 7.0 Landers Aftershock
>

Preliminary Report: The Hector Mine Earthquake,
10/16/1999

A M7.0 earthquake occurred at 2:46 a.m. local time on 10/16/1999. The event was
located in a remote, sparsely-populated part of the Mojave desert, approximately
47
miles east-southeast of Barstow and 32 miles north of Joshua Tree. The event is
not
considered an aftershock of the M7.3 Landers earthquake of 1992, although
subsequent analysis will explore the relationship between these two events.
Preliminary results do indicate that the Hector Mine Earthquake occurred in a
region
where stress was increased by the 1992 Landers earthquake.

On average, an earthquake of M7.0 is expected to generate approximately seven
aftershocks of M5 or larger within the first week. The largest early aftershock
was a
M5.3 event at 2:49 local time. A M5.8 aftershock occurred at 5:57 a.m. local
time
with an epicenter approximately 15 kilometers south of the mainshock. A third
event
with M5.0 occurred at 10:38 a.m. As of noon on 10/16, 18 aftershocks of M4 or
larger have occurred.

The earthquake occurred near the Pisgah fault, which strikes north-northwest
through the eastern Mojave shear zone. Scientists with Caltech and the US
Geological
Survey are continuing to analyze the data to determine whether or not this fault
was
associated with the earthquake. Geologists are heading to the epicentral area to
look
for surface rupture, which is expected for an earthquake of this magnitude.
(Updated
12:05 p.m., 10/16/99)