July 3 1999 (July 2 local time) Satsop Earthquake

Basic Information

Time of Occurrence (GMT): Saturday July 3, 1999 at 01:43:54.33 Z
Time of Occurrence (PDT): Friday July 2, 1999 at 06:43:54.33 PM
Time of Occurrence (PST): Friday July 2, 1999 at 05:43:54.33 PM

Depth (km) 40.57
Magnitude: Mw=5.8 (Harvard CMT)
Other magnitude estimates: MS=5.5, mb=5.5, Mc=5.1

Location 47.0757N 123.4635W
     8.2 km   N of Satsop, WA
    28.9 km ENE of Aberdeen, WA
   103.5 km WSW of Seattle, WA

Name of data file: 99070301435p

A Note on The Magnitude

The magnitude estimation routinely used by the Pacific Northwest Seismograph Network is Mc or "Coda magnitude". Although the coda magnitude scale works well for small and moderate size earthquakes it has not been well calibrated for deep and large earthquakes. In order to do a better job of comparing this earthquake with other large earthquakes around the world it is useful to determine the magnitude using other methods commonly used for large earthquakes. Coda magnitude for the Satsop earthquake is Mc 5.1

Other magnitude scales include the body wave magnitude (mb), surface wave magnitude (Ms) and moment magnitude (Mw). Other agencies including the National Earthquake Information Center, and Harvard University have computed the following estimates of magnitude for this earthquake: mb=5.5, Ms=5.5, and Mw=5.8.

Earthquake Felt Reports for the Main Shock


Summary of Felt Reports received for this earthquake (includes an intensity map).

Aftershocks

Normally, deep earthquakes have very few significant aftershocks. This earthquake had no detectable aftershocks for several days. On July 9, 1999 we recorded 3 small aftershocks with epicenters and depths almost identical to the main shock. They included earthquakes at 05:13UT (Mag 1.6), 07:45UT (Mag 2.5), and 08:07UT (Mag 2.3).


Detailed Information and Graphics for the Main Shock

Our data base of earthquake hypocenters contains information from the 19th century to the present. Included are:

Earthquake Mechanism

If sufficient P-wave first motion data are available, a fault plane determination for the earthquake will be available in the form of

Moment Tensor Estimates of the Earthquake size may also be available. To see, check at Oregon State U.

Preliminary Strong Motion Information

Related Information: Most Up-to-Date Local, National, and Global Earthquake Summaries