Summary of examples of correlation between lithology and seimicity Jessica Hawthorne Ge277 February 26, 2014

Outline Mostly aseismic with small earthquakes – Costa Rica – Nankai – SAF – Zuccale

More clay: – More velocity-strengthening at low slip speeds – Lower absolute strength Ikari et. al., 2011

Ikari et. al., 2013 Northwest: – Cold – Few seamounts – Larger earthquakes Southeast: – Hot – Seamounts – More small earthquakes Wang and Bilek, 2011

Hemipelagic ooze: Weak, mostly velocity-strengthening Nanofossil chalk on seamounts: Strong, velocity-weakening A recipe for small earthquakes?

Zuccale Fault Niemeijer and Collettini, 2013 Low-angle normal fault in northen Appenines Nearby faults have shallow microseismicity Misorientation suggests low effective friction

Pink and orange: -Less talc, more quartz -More unstable

-Less stable deeper -Small earthquakes on velocity-weakening patches

Nankai accretionary prism Ikari and Saffer, Evidence that splay fault ruptured to the trench -Low frequency earthquakes along splay faults

Ikari and Saffer, 2011 Mostly velocity-strengthening Increase in a-b with slip rate mostly results from decrease in b Suggests it’s hard to rupture seismically

Ujiie and Tsutsumi, 2010 Strong velocity weakening at higher slip rates From thermal pressurization

Tsutsumi et. al., 2011 Some samples are v-w even at low slip rates Would allow for small earthquakes

San Andreas Fault Irwin and Barnes, 1975 Creep and microseismicity coincident with serpentinite at the base of the Great Valley sequence? Locations from Waldhauser and Schaff, 2008

Reinen et. al., 1994

So can lithology explain the observed distribution of earthquakes? Maybe 4 locations that are consistent, but not compelling Clays generally stable at low slip speeds Can be unstable at high slip speeds Most instability added with more quartz or calcite