HR: 1340h
AN: S23B-0249    [Abstracts]
TI: Earthquake Magnitude and the Length of Mid-Ocean Ridge Segments
AU: * Clark, A
EM: clarkam@eckerd.edu
AF: Eckerd College, Department of Marine Science, Saint Petersburg, FL 33711 United States
AU: Wetzel, L R
EM: wetzellr@eckerd.edu
AF: Eckerd College, Department of Marine Science, Saint Petersburg, FL 33711 United States
AU: Frohlich, C
EM: cliff@utig.ig.utexas.edu
AF: Institute for Geophysics, University of Texas, Austin, TX 78759 United States
AB: Seismic moment is known to depend on fault length. Thus, it would be expected that the largest earthquakes on mid-ocean ridges and transform faults would occur on the longest segments. Observations of seismicity on oceanic ridges and transforms, however, suggest that there is a limit to earthquake size. Magnitudes increase up to a critical segment length, past which earthquake size does not increase with segment length. In this study, oceanic ridges and transforms are delineated as segments greater than 1 km in length and are defined relative to plate motions calculated using the NUVEL-1A plate model. A minimum magnitude of 5.5 was used from the Harvard CMT catalogue to ensure complete global coverage. On transform fault segments, maximum earthquake magnitudes increase from approximately 5.5 to 7.0 as segment lengths increase to 100 km; past this point maximum magnitude does not increase. In a similar manner, on ridge segments there is an increase in maximum magnitude with length up to approximately 80 km. Unlike transforms, however, there is a slight decrease in maximum magnitude at greater lengths. To compliment the analysis of all earthquakes greater than M 5.5, we also assessed the maximum magnitudes expected using the assumption that magnitudes satisfied a Gutenberg-Richter relationship. When binned together in 10 km intervals, smaller ridge and transform segments display observed maximum magnitudes that are significantly lower than expected. As length increases to approximately 230 km, the gap decreases between the actual and expected magnitudes.
DE: 3035 Midocean ridge processes
DE: 3039 Oceanic transform and fracture zone processes
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7245 Mid-ocean ridges
DE: 7250 Transform faults
SC: Seismology [S]
MN: Fall Meeting 2005