Seismo-Watch Significant Earthquake Report - No. 01-038
Regional Location:

Preliminary Magnitude:

Greenwich Mean Date:
Greenwich Mean Time:
Focal Depth:


Ml 5.2 (NEIC), ML 4.2 (HVO)

13:11:44 (03:11 a.m. local time)
10.0 km, Fixed

HAWAI'I, SEPTEMBER 13, 2001 (Seismo-Watch) -- A robust earthquake swarm has been detected off the southeastern coast of Hawai'i at the Lo'ihi Seamount.

It began with a Ml 5.0 (NEIC), ML 4.7 (HVO ) earthquake at 2:09 p.m. HST on Monday, September 10, in the Pacific Ocean about 27 miles southeast of Na'alehu at the Lo'ihi Seamount. It was followed by a robust swarm that included six M3s on the 10th and one M3.4 on the 11th. Activity this far off the coast is limited to activity in the M2+ range.

Then at 3:11 a.m. HST, a M5.2 (NEIC), M4.9 (HVO) earthquake shook the Lo'ihi Seamount. It was followed by some 5.5 hours by a tremor measuring M4.2 at 8:40 a.m. There have been no indication of an aftershock sequence at this time.

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This was the most severe swarm at Loihi since July 1996, when the summit of the Lo'ihi Seamount collapsed.

There was no indication of increased volcanic activity at Kilauea.

Felt Reports
Although it is likely the temblors were felt along the southeastern coast of Hawai'i, there have been no official reports at this time.

From the Global Volcanism Network:

Lo'ihi seamount, the youngest volcano of the Hawaiian chain, lies about 35 km off the southeast coast of the island of Hawaii'. Lo'ihi (which is the Hawaiian word for "long") has an elongated morphology dominated by two curving rift zones extending north and south of the summit.

The summit region contains a caldera about 3 x 4 km wide and is dotted with numerous lava cones, the highest of which is about 975 m (3,100 ft) below the sea surface.

Deep and shallow seismicity indicate a magmatic plumbing system distinct from that of Kilauea volcano. Abundant fresh, sediment-free lavas and low-temperature hydrothermal venting attest to the youthful age of the volcano.

During 1996, a new pit crater was formed at the summit of the volcano, and lava flows were erupted. Continued volcanism is expected to eventually build a new island at Lo'ihi; time estimates for the summit to reach the sea surface range from roughly 10,000 to 100,000 years.

Additional seismic information links:

Mainstream media news reports:
  • None at this time.
Report update: 9:48:16 AM, Wednesday, September 19, 2001
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