HR: 0800h
AN: T21C-0494    [Abstracts]
TI: Parameters Affecting Seismic Moment Release Rates Along Plate Boundaries
AU: * Frohlich, C
EM: cliff@utig.ig.utexas.edu
AF: University of Texas at Austin, 4412 Spicewood Spr Bldg 600, Austin, TX 78759 United States
AU: Wetzel, L R
EM: wetzellr@eckerd.edu
AF: Eckerd College, 4200 54th Ave S, St. Petersburg, FL 33711 United States
AB: We have undertaken a survey of seismic moment release along Earth's major plate boundaries. For each plate boundary, the moment release rate R is the sum of scalar moments divided by the length of the boundary and by the relative plate velocity V; we evaluate R for both the Harvard CMT and a global historical catalog. The survey confirms that values of R differ systematically among different categories of plate boundaries; typically R is lowest for divergent boundaries; about a factor of ten larger for transform boundaries; and another factor of ten larger for convergent boundaries boundaries. For both transform and divergent boundaries R depends strongly on the relative velocity V; boundaries with V less than about 4 cm/yr release moment at rates 2-10 times greater than boundaries with faster rates. Generally, measured values of R are about the same for oceanic and continental boundaries that have similar relative velocities. At convergent boundaries, we also evaluate moment release rates for earthquakes having different focal depths. Preliminary results indicate that in depth ranges where earthquakes do occur, the rate doesn't vary systematically for earthquakes with depths between about 100 and 600 km; however, the rates for the earthquakes deeper than 50 km are at least 2 orders of magnitude less than for the shallow events. For the deeper earthquakes this suggests that less than 1% of the lithospheric motion is expressed seismically. Within each tectonic environment considered there is scatter of about a factor of ten in the measured moment release rates. Although it is plausible that this scatter occurs because the rare, large earthquakes possess most of the moment, most of the scatter remains when we calculate moment release rates using methods that are insensitive to rare large events. Our presentation will include speculation about what might be responsible for this scatter.
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8150 Plate boundary: general (3040)
SC: Tectonophysics [T]
MN: Fall Meeting 2005