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Anatahan Volcano Update, June 27-July 1
July 1, 2003
08:00 A.M. Pacific/Saipan (GMT+10 hours)
We made no direct observations of Anatahan during this reporting period, since
tremor levels were so low. There also were no reports about activity from
commercial pilots or fishermen. We plan to take the helicopter to Anatahan on
July 2.
Seismicity
We continue to monitor hourly tremor amplitudes from the analog record. Since
June 27, tremor levels have decreased, without significant episodes of banding.
A rough relation between Earthworm digital counts and amplitudes determined from
the drum record has been established. Values range from about 70 counts/mm at
2.5 mm, to 55 counts/mm at 10 mm and 45 counts/mm at 30-50 mm peak-to-peak
amplitude.
The new seismic station planned for Sarigan requires both overwater and
helicopter transport for station components, cement, and fuel. Sarigan is at the
limit of helicopter range from Saipan. Work is expected to start in about a
week.
The following earthquakes were recorded at the Anatahan station for the period
June 27-July 1:
Local time at Anatahan S-P time
Maximum amplitude Notes
(seconds) (mm, peak-to-peak)
6/27/2003 00:10:40.62 5.0
28
Estimated magnitude – 2.5
6/27/2003 06:59:03.10 5.5
12
Double event,
magnitude < 2
6/28/2003 17:25:45.70 25.6
clipped
USGS/NEIC: 20 mi. N of
Pagan, depth 144 km
magnitude 4.4mb
6/29/2003 05:11:06.79 >60
28
USGS/NEIC: 30 mi. W of
Agrigan, depth 584 km
magnitude 4.6mb
6/30/2003 05:22:43.16 14.2
10
Appears long-period
6/30/2003 11:19:42.60 5.0
18
Estimated magnitude - 2
Graph showing the peak and average hourly tremor amplitude values June
16-30, 2003.
Contact persons:
Juan Takai Camacho, Geophysical Seismic Technician, EMO Saipan; tel:
(670) 322-9528, fax: (670) 322-7743, email: juantcamacho@hotmail.com
Ramon Chong, Geophysical Instrument Specialist, EMO Saipan; tel: (670)
322-9528, fax: (670) 322-7743, email: rcchongemo@hotmail.com
Frank Trusdell, Geologist, USGS; tel: (808) 967-8812, fax: (808) 967-8890,
email: trusdell@usgs.gov
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