Earthquakes in the Ocean: Where, Why, and What Happens? As prepared for ESCI Earth Structure & Deformation And Sally Ride Festival, Houston (10/25/06) Prof. Julia Morgan Dr. Meghan Miller Department of Earth Science Rice University

Dale Sawyer’s Discovering Plate Boundaries Exercise ( An aside: Designed for students to observe & classify Appropriate for broad range of ages/exper. Designed for 3 days, w/ variations Excellent framework for MARGINS & similar

Seismology Map – Earthquake Locations and Depths

Volcanology Map – Recent Volcanic Activity

Geochronology Map – Seafloor Age

Geography Map – Topography and Bathymetry

Plate Boundary Map

Where do all the earthquakes occur?? (Press et al., Understanding Earth, 4th Ed.)

Kurile Earthquake Nov. 15, 2006 Juli

Tectonic Setting - Kuriles Subduction of Pacific Plate Plate beneath Okhotsk/N. America. Conv. rate: ~ 9 cm/yr. Sakhalin Island & Japan are rifted cont. Political Setting Russia “stole” from Japan after WW II

Kurile Earthquake Nov. 15, 2006

Kurile Tsunami - Nov. 15, 2006

Convergent Boundaries: Three Types Ocean-ocean Sumatra earthquake! M ~9.3 (2004) Ocean-continent Chile earthquake! M ~9.5 (1960) Continent-continent South Asian earthquake! M ~7.5 (2005) In the Oceans (Press et al., Understanding Earth, 4th Ed.)

M 9.5 Earthquake (Largest worldwide) Rupture zone ~1000 mi long. Rupture zone ~1000 mi long. Generated a tsunami that spread across Pacific. Generated a tsunami that spread across Pacific. Run-up: 25 m in Chile; 10.7 in Hilo; 1.7 in CA. Run-up: 25 m in Chile; 10.7 in Hilo; 1.7 in CA. ~ 6000 people died, most from tsunami. ~ 6000 people died, most from tsunami. $3.5 Billion property damage $3.5 Billion property damage Chile - 5/22/1960 (Source: Sawyer, Discovering Plate Boundaries)

M 9.2 Earthquake (3rd or 4th largest worldwide) 750 mi long rupture zone. 750 mi long rupture zone. Large landslide and tsunami across Pacific. Large landslide and tsunami across Pacific. Ground displacements 25 ft x 3 ft. Ground displacements 25 ft x 3 ft. 122 people died worldwide, most from tsunami. 122 people died worldwide, most from tsunami. Property damage $500 million. Property damage $500 million. Alaska - 3/27/1964 (Source: Sawyer, Discovering Plate Boundaries)

Alaska Tsunami (Press et al., Understanding Earth, 4th Ed.)

M 9.3 Earthquake (2nd largest worldwide) 1000 km long fault rupture km long fault rupture. Generated a tsunami that went around the world. Generated a tsunami that went around the world. No warning. No warning. More than 200,000 people died. More than 200,000 people died. Untold property damage…. Untold property damage…. Southeast Asia - 12/26/2004 (Source: Sawyer, Discovering Plate Boundaries)

Sumatra Earthquake Fault zone rupture ~ 1000 km in length Epicenter Sumatra Indian Plate (Source: USGS)

What is a tsunami & How does it form? A sudden impulse pushes the water, forming a train of waves that spreads outward from the source. Tsunami front propagates at ~450 mi/hr (~600 km/hr). (Source: Prof. Miho Aoki, U. Alaska Fairbanks)

Tsunami Generation & Propagation Sumatra Tsunami (12/26/04) - red: rise in sea level - blue: fall in sea level (

What Happens Nearshore? As the water column shallows, wave height grows. Tsunami run-ups can be MUCH larger than original wave. (Press et al., Understanding Earth, 4th Ed.)

What are the Consequences? Coastal damage and destruction. (Source: Prof. Miho Aoki, U. Alaska Fairbanks)

Can This Happen in N. America? Yes!!

M ~9 Cascadia Earthquake (7th largest?) No historic record in North America. No historic record in North America. Recorded in Japan ~9 hrs later. Recorded in Japan ~9 hrs later. Tsunami deposits found along Oregon coast. Tsunami deposits found along Oregon coast. Recurrence interval is yrs! Recurrence interval is yrs! Oregon-Washington - 1/26/1700 (Source: Sawyer, Discovering Plate Boundaries)

January 1700 Cascadia Tsunami (Source: K. Satake,

Where do Great Earthquakes occur? Seismogenic Zone Coseismic Slip Aseismic Slip Tsunamigenic Slip Plate boundary mega-thrust SedimentsRocks Why do Great Earthquakes occur?

Where can we study great earthquakes? Nankai Trough Subduction of the Philippine Sea Plate beneath Eurasia. Convergence rate: ~4 cm/yr. Thick clastic-rich sediment section (hemipelagites and turbidites).

Earthquake Recurrence Nankai margin is subject to repeated large (M ~ 8) earthquakes. Evidence for tectonic segmentation of the margin. Earthquake recurrence ~180 yrs. -> There will be future earthquakes!! (Ando, 1975)

Co-seismic Slip Zone (Bangs et al., 2004) Up-dip limit

Recent Ocean Drilling & Surveys

Toe of Muroto Transect Decollement 1 km Proto-decollement Deformation front Proto- thrusts Frontal thrusts NANKAI TROUGHNANKAI PRISMPROTO-THRUST ZONE Depth (m) Trench Fill turbidites Shikoku Basin Strata hemipelagic sediments Ocean Crust

(J.C. Moore and Saffer, 2001) Prism Architecture Décollement partitions the incoming section: - Accreted section vs. underthrust section. Décollement steps down near the updip limit. Seismogenic ZoneCoseismic ZoneAseismic Zone (after G.F. Moore et al., 2001) Up-dip limit

Décollement Amplitude (Bangs et al., 2004) Downdip decrease in décollement amplitude. Suggests dewatering of underthrust section.

(J.C. Moore and Saffer, 2001) Pore Fluid Pressures Modeled pore fluid pressures are highest near up-dip limit. (after G.F. Moore et al., 2001) Seismogenic ZoneCoseismic Zone Updip limit

Seismic-Aseismic Transition -> Onset of Earthquakes Coincident with onset of coseismic sliding: – Out of sequence thrust. – Step down in décollement. – Reduced décollement amplitude. – Increased pore fluid pressures. Why? Something changes along décollement: – Frictional behavior: stable vs. unstable? –Loss of strength in underthrust sediments? –Something completely different? Future fault zone drilling may tell us….