SPECIAL EARTHQUAKE

Special Event

Basic Information

Time of Occurrence (GMT): Wednesday October 21, 1998 at 05:25:24.92 Z
Time of Occurrence (PDT): Tuesday October 20, 1998 at 10:25:24.92 PM
Time of Occurrence (PST): Tuesday October 20, 1998 at 09:25:24.92 PM

Depth (km) 9.36
Magnitude (Mc) 3.1

Location 45.9403N 122.0785W

    30.0 km SSE of Mount St. Helens
    36.9 km   S of Spirit Lake
    61.7 km  NE of Portland, OR

Name of data file: 98102105252c

This is an automated web page produced after a significant earthquake to give essential information about the earthquake and previous earthquake activity in the region. This information will be updated as needed.

Detailed Information and Graphics about the Earthquake

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

A regional map showing the location of the earthquake (in red) plus previous earthquakes M > 3.5 since 1990.
A Intermediate scale map showing the location of the earthquake and prior historical earthquakes with magnitude 3.5 or greater.
A list of 10 big earthquakes preceding the mainshock that are closest to it and have a magnitude greater than 3.5. These are the most significant historical earthquakes in the vicinity of the mainshock (see intermediate scale map above).
A map showing the location of the earthquake relative to cities.
A map showing the location of the earthquake relative to the nearest seismograph stations that recorded it.
A detailed list of all earthquakes (M > 1.0) that occurred in the vicinity of the special earthquake in the previous two years. For the locations of these events see the next map.
A map of all earthquakes (M > 1.0) that occurred in the two years prior to the special earthquake. Detailed area shown is just few kilometers around the mainshock.
A List of the nearest 20 strong motion sites

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

A diagram of the fault plane solution(s). In some cases more than one solution may fit the data.
A table describing the fault plane solution(s) summarizing the characteristics of possible fault planes ("A" and "B") that are consistent with the recorded first-motion data.

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

Moment-Tensor Web site at Oregon State University

Preliminary Strong Motion Information

Strong-motion information from digital accelerographs.

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

Catalog and Map of Pacific Northwest earthquakes, Mag>2 from the PNSN
Catalog and Map of United States earthquakes, from the ANSS
Catalog and Map of world earthquakes, from the IRIS