Special Earthquake Report .
Klamath Falls M 4.3 earthquake

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Wednesday, May 15, 2002

An earthquake measuring M 4.3 occurred late this morning at 10:54 a.m. PDT in southern Oregon, but there have been no reports of damage or injuries at this time.

Preliminary data from the United States Geological Survey's (USGS) Advanced National Seismic System (ANSS) indicated the temblor occurred at 17:54:47 UTC or 10:54 PDT and was centered about 12 miles northwest of Klamath Falls and 9 miles north-northwest of Altamont along the southwestern shore of Lower Klamath Lake, near Potter Butte. See a Topozone location map. See USGS-ANSS location map.

The focal depth was fixed at 8.1 km (5 miles) for quick data processing. Analysis by UC Berkeley determined a Moment magnitude of (Mw) 4.3, which is comparable to the Duration magnitude of (Md) 4.3. Their fault plane solution indicated predominately normal slip motion (down and away or extensional movement) along a northwest trending plane.

It was followed by a small M 1.4 aftershock about five minutes later, which passed without any reports.

It is not know at this time which fault caused the earthquake.

The quake was sharply felt at Klamath Falls where windows shook, walls vibrated and hanging plants swung. It was described as a swift jolt, followed by a rolling motion that had sharp vibrations. It was felt as far away as Ashland and Medford to the west and Tulelake, California to the south. See USGS Community Intensity Map (CIIM).

One person said the shaking caused their internet connection to terminate and they needed to log back in.

This was the largest quake in the Klamath Falls area since 1994. On September 21, 1993, two strong earthquake measuring M 6.0 and M 5.9 occurred a few miles to the west in the Mountain Lakes Wilderness Area, causing widespread moderate damage in the area. See list of earthquakes since 1990.

The quake comes a little more than 10 hours after a M 5.4 temblor occurred about 140 miles off the coast of Coos Bay, Oregon, along the southern segment of the Blanco Fracture Zone. See USGS-NEIC information sheet.

Report update: 7:33:26 AM, Thursday, May 16, 2002
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