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Volcanowatch

March 15, 2001

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.


Professor Fusakichi Omori - an instrumental person at HVO

The U.S. Geological Survey's Hawaiian Volcano Observatory currently operates a network of 65 seismic stations. Signals from each station, including the four on Maui, are radio-telemetered to HVO and recorded. When an earthquake is detected, the arrival time of the earthquake at each station is timed, and an epicenter is determined within a few seconds. It takes a few minutes longer to calculate a magnitude. Then the location and magnitude of the event are posted on our web site (http://hvo.wr.usgs.gov).

The present high-tech seismic operation at HVO had a humble beginning 92 years ago. In his preparation for establishing a volcano observatory, Thomas A. Jaggar traveled to Japan in 1909 to learn about Japanese seismological methods. He met with Professor Fusakichi Omori, head of the Seismological Institute of the Tokyo Imperial University. Thus began a long friendship that lasted until Professor Omori's death in 1923. HVO greatly benefited from this personal relationship.

The meeting in Japan resulted in the presentation to Dr. Jaggar of an Omori seismograph, various seismological publications, and a set of construction plans for a seismic vault. When the original HVO was built at the site of the present Volcano House hotel, a basement was dug, and the Whitney Seismological Laboratory was constructed in accordance with the plans of Professor Omori. The first instrument installed was the Omori seismograph, followed a year later by two Bosch-Omori seismographs purchased by the Massachusetts Institute of Technology. These instruments were entirely mechanical, with amplification of the horizontal ground movement dependent upon the length of the weighted pendulum arm.

Variations of these instruments were the main seismic detectors for 40 years until 1953, when electromagnetic sensors were introduced. One instrument, which was also used for tilt measurements, however, remained in operation until 1963, when the Whitney vault was abandoned. The National Park Service is now in the process of restoring the vault and reestablishing the seismographs.

In addition to his seismographs, HVO used the methodology developed by Professor Omori to locate earthquakes. The tables or traveltimes of different earthquake waves published by Professor Omori were ideal for locating local Hawaiian earthquakes. Of greater importance to HVO were the publications describing the physical, petrologic, geodetic and seismometric data of Japanese volcanic eruptions by Professor Omori and his colleagues.

Professor Omori's accounts of the 1914 eruption of Sakurajima Volcano are classic. The description of the eruption, earthquake activity, ground deformation, gases, eruptive products and societal concerns are covered. Jaggar patterned his volcano monitoring efforts to detect precursory signals reported by Professors Omori and Koto.

The technology and techniques used to monitor volcanoes today may have changed, but the precursory phenomena remain the same. Thomas A. Jaggar would be proud if he could now see the Observatory that he established and the earthquake monitoring program built upon his friendship with Fusakichi Omori. But he wouldn't be surprised by our rapid detection and reporting capabilities; he foresaw that in 1941!

Eruption Update

Eruptive activity of Kilauea Volcano continued unabated at the Pu`u `O`o vent during the past week and provided visitors with an occasional glimpse of surface flow activity on Pulama pali and on the coastal flats. Lava is pooling in the coastal flats and not entering the ocean at this time. The broad active flow front extends 1.5 km (0.9 mi) to the west from the end of the Royal Gardens private access road. A small lobe of the flow front is now only 0.3 km (0.2 mi) from the sea coast.

One earthquake was reported felt during the week ending on March 15. Residents of Pahala and Hawaiian Ocean View Estates felt an earthquake at 5:05 a.m. on Sunday, March 11. The magnitude-3.4 earthquake was located 4 km (2.4 mi) north of Pahala at a depth of 6.5 km (3.9 mi).


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Updated: March 19, 2001