HR: 1330h
AN: V12B-0583    [PDF]
TI: Microearthquakes Near Matua Seamount, GLIMPSE Study Area
AU: * Llenos, A L
EM: Andrea_Llenos@brown.edu
AF: Brown University, Dept. of Geological Sciences, Brown University, Providence, RI 02912 United States
AU: Forsyth, D W
EM: Donald_Forsyth@brown.edu
AF: Brown University, Dept. of Geological Sciences, Brown University, Providence, RI 02912 United States
AU: Webb, S C
EM: scw@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, L-DEO Route 9W, Palisades, NY 10964 United States
AB: As part of the GLIMPSE Experiment, we deployed five ocean-bottom seismometers (OBS) in an array on the flanks of Matua Seamount, about 400 km west of the East Pacific Rise. Matua stands about 2000 m above the surrounding seafloor and is surrounded by a number of smaller volcanic cones and recent lava flows, as indicated by highly reflective seafloor imaged by side-scan sonar and by fresh basalt samples dredged from the flows. The array, measuring about 20 km across, was deployed for about 30 days in November and December, 2001. Record quality varied; two of the three-component OBSs were much noisier than the others, but the largest events were recorded at all 5 stations. One event was recorded by a sixth OBS, deployed for a short time as part of a nearby refraction experiment. The microearthquake activity confirms the impression given by the side-scan sonar data that Matua Seamount is still an active volcano. P and S waves from sixteen events were recorded well enough by three or more stations to obtain hypocentral estimates. We used a grid-search technique to both locate the earthquakes and to obtain full, non-linear estimates of the uncertainty in location. All of the events are located north or east of Matua, most in the vicinity of recent lava flows. None are beneath the primary edifice itself. Nine of the earthquakes are in very shallow, upper crust. Two are near the base of the crust and five are in the mantle at depths of 12 km or more below the seafloor. The relatively great depths of the mantle events provide an important constraint on the mechanical properties of the 6 Ma old lithosphere on which Matua is constructed.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 7218 Lithosphere and upper mantle
DE: 7220 Oceanic crust
DE: 7280 Volcano seismology (8419)
DE: 8120 Dynamics of lithosphere and mantle--general
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting