HR: 1330h
AN: V52B-0425    [PDF]
TI: 3-d Visualization of Earthquakes and Erupting Vents in Time-series Animations: Application to Kilauea and Miyakejima volcanoes
AU: * Wright, T L
EM: twright@usgs.gov
AF: U.S. Geological Survey, University of Tokyo Earthquake Research Institute, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AB: Computer programs have been developed to view erupting vents and earthquake sequences on and beneath transparent topography shown by a DEM, vertical image, or map. In a single frame an earthquake dataset can be rotated with the mouse to create perspective views. Multiple-frame time animations are created in which the perspective (e.g., map, cross-section) and time increments (e.g., hour, day, month) are chosen by the user. Viewed as movies, the animations allow recognition of seismicity patterns occurring over large areas and long time periods. Departures from characteristic activity are easily spotted and can be further investigated in a single frame or in animation with shorter time increments. Time animations have been made of earthquake sequences accompanying several eruptions of Kilauea volcano and the Miyakejima eruption and associated dike emplacement in 2000. An earthquake swarm shallower than 6 km beneath Miyakejima island began on the evening of 6/26/2000. The seismicity moved to the southwest, then to the north and offshore, and a submarine eruption occurred on the morning of 6/27. Shortly thereafter, earthquakes of M 4 and above migrated westward, also becoming deeper (to 20 km), marking the emplacement of a large dike northwest of Miyakejima island. Eruptions at Miyakejima from 7/8 to 9/1 were associated with formation of a new caldera. The timing and location of the submarine eruption can be seen in the seismicity, consistent with later visual observation of discolored seawater and photographs obtained of the seafloor vents. Seismicity associated with the submarine eruption plunges eastward. Seismic sequences preceding explosive eruptions at Miyakejima summit in August plunge southwest. Intersection of the opposed dips occurs near 10 km depth, consistent with existence of a deeper basaltic reservoir feeding the explosive eruptions. Sequences of vertical, pipe-like seismicity extending to very shallow depths over the propagating dike and occurring over times of 4-6 hours suggest additional episodes of undersea eruption near the islands of Kozushima and Toushima. At Kilauea the focus has been on two long eruptions, Mauna Ulu (1969-1974) and Pu'u 'O'o (1983-ongoing). In the latter a maturing magma transport system is shown by (1) diminishing shallow rift seismicity and south flank response, and (2) increasing frequency and depth of long-period seismicity beneath Kilauea's summit. An event seen in the animations and not previously noticed was a seismic sequence beneath Kilauea triggered by the M6.6 Mauna Loa earthquake of 11/16/1983. Beginning 4 hours after the mainshock, seismicity occurred on a Kaoiki fault trace buried beneath Kilauea lava and also on Kilauea's southwest flank, a zone usually active only during intrusions on Kilauea's southwest rift zone. In the former the animations vividly depict the changing seismicity beneath the growing Mauna Ulu shield and the eruptions and intrusions elsewhere on the volcano that occurred during pauses in the Mauna Ulu activity. Following the end of Mauna Ulu activity in 7/1974, the animations show the sequence of eruptions and intrusions leading up to the M7.2 Kilauea south flank earthquake of 11/29/1975. The presence of greatly elevated levels of seismicity at 30 km beneath Kilauea and at 0-15 km beneath Kilauea's southwestern flank compared to earlier times may be useful in forecasting future large south flank earthquakes. The same computer programs used for the volcano animations can be applied to mainshock aftershock sequences associated with large earthquakes, and to tectonic earthquake sequences associated with subducting or obducting plates.
DE: 1734 Seismology
DE: 1749 Volcanology, geochemistry, and petrology
DE: 1794 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting