EARTHQUAKE SWARM at MOUNT HOOD

EARTHQUAKE SWARM AT MOUNT HOOD, OREGON

Basic Information

A Swarm of earthquakes began at Mount Hood on January 11, 1999. A current list of earthquakes in the swarm is available. In general the earthquakes occurred about 4 miles (7 kilometers) south-southeast of Mount Hood near the Mount Hood Meadows ski area. Several magnitude 3 earthquakes have occurred in the swarm. The largest earthquake in this area in the last 30 years was a magnitude 4 earthquake on December 13, 1974. The approximate location of earthquakes in the January, 1999 swarm is 45.3195N 121.6538W.

This is an automated web page produced after a significant earthquake to give essential information about the earthquake, its aftershocks, and previous earthquake activity in the region. Some of the information here will be updated -- See the section on Aftershocks.

Detailed Information and Graphics about the Earthquake

(Also visit our section on General Information about Mount Hood)

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 mainshock (in red) plus previous earthquakes M > 3.5 since 1990.
A Intermediate scale map showing the location of the mainshock and prior historical earthquakes with magnitude 3.5 or greater.
A SPECIAL MAP showing the January, 1999 swarm in relation to previous earthquakes (M>1) in the last 20 years.
A list of 10 big earthquakes preceding the mainshock that are closest to it and have a magnitude greater than 4.0. 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 mainshock relative to cities.
A map showing the location of the mainshock relative to the nearest seismograph stations that recorded it.
A general map of significant historical earthquake locations in the Pacific Northwest.
A detailed list of all earthquakes (M > 1.0) that occurred in the two years prior to the mainshock in the area shown on the next map
A map of all earthquakes (M > 1.0) that occurred in the two years prior to the mainshock. Detailed area shown is just few kilometers around the mainshock.
A List of the nearest 20 strong motion sites

Foreshocks and Aftershocks

The following information will be updated as new aftershocks occur. Included are:

An Earthquake Catalog listing the location and magnitude of all earthquakes we have located in the epicentral region (including the mainshock and any aftershocks) for the current year.
Detailed Map of the earthquakes in this catalog for the epicentral region.
Seismic Activity as a function of time in the epicentral region since the time of the mainshock.

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