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External Control of Seismicity from the Shaping of Active Tectonic Compared to Passive Continental Margins: Influences from Reservoir Development

Nelson, Hans 1; Goldfinger, Chris 2; Guttierrez Pastor, Julia 4; Morey, Ann 3; Escutia, Carlota 4
1 University of Texas at Arlington, Arlington, TX.
2 Oregon State University, Corvallis, OR.
3 Oregon State University, Corvallis, OR.
4 University of Granada, Granada, Spain.

Correlation of synchronously triggered Holocene turbidites for up to 1000 km and along continental margins off western North America, using stratigraphic markers (i.e. ash, biostratigraphy), high-resolution radiocarbon ages and physical property signatures (i.e. density, magnetic susceptibility), implies seismic triggering by great earthquakes (> 8 Mw). The following important new observations about turbidite and mass transport deposition (MTD) can be attributed to seismic triggering: (1) On the tectonically active Cascadia subduction zone and San Andreas transform fault margins (approximately every 500 and 200 years respectively) triggering of turbidity currents is dominantly controlled by earthquakes, versus other generating mechanisms (e.g. storms, random failures). (2) Turbidite deposition continues during sea level highstands on active margins. (3) The paleoseismic turbidites exhibit multiple coarse pulses caused by margin rupture patterns and synchronous triggering in multiple tributary canyon sources. (4) Along the Cascadia and California margins, turbidite systems are dominant and MTDs are subordinate; we attribute this difference to frequent seismic triggering that causes seismic strengthening of sediment. The frequent shaking by great earthquakes dewaters and densifies sediment, which reduces sediment mobilization during sediment failures. As a result, maximum run-out distances of mass transport deposits across basin floors are approximately an order of magnitude less in active (maximums of 100 km) compared to muddy passive margins (maximums of 1000 km) (5) MTDs are less common and less intermixed with turbidites in basin floor turbidite systems of active tectonic margins compared to passive margins. Consequently, MTD baffles and seals are less common in basin floor turbidite systems of active tectonic compared to passive margin settings.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009