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Jaime Andres Convers Dr. Andrew Newman Earth & Atmospheric Sciences

The global seismic energy to moment ratio: a tool for basic research and real-time identification of “Tsunami Earthquakes”. Jaime Andres Convers Dr. Andrew Newman Earth & Atmospheric Sciences. Motivation. Recent increased activity of large earthquakes

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Jaime Andres Convers Dr. Andrew Newman Earth & Atmospheric Sciences

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  1. The global seismic energy to moment ratio: a tool for basic research and real-time identification of “Tsunami Earthquakes” Jaime Andres Convers Dr. Andrew Newman Earth & Atmospheric Sciences

  2. Motivation • Recent increased activity of large earthquakes • Methods for rapid assessment of earthquake size have not been adequate for Tsunami potential • Rapid assessment is important for hazard mitigation from strong shaking and Tsunami generation • Identify slow tsunami earthquakes • Obtain a discriminant for tsunami earthquakes for use in real time

  3. Tsunamigenic Earthquakes: Shallow events in subduction zones Generate observable Tsunami Tsunami Earthquakes: Shallow events in subduction zones Generate observable Tsunami, larger than expected for its size Slow rupture Deficient in high frequency energy Tsunami Earthquakes (TsE) pubs.usgs.gov/

  4. Energy to moment ratio • Measure of how much seismic energy is radiated related to the size of its corresponding earthquake. • Theoretically θ assumed constant (constant stress drop). • TsE are deficient in energy at high frequencies • Useful for identifying energy deficient TsE

  5. Core Mantle Global Catalog • Mw>6.6 from 1997+ • Radiated seismic energy in vertical component • Between 30º and 80º. • Above 30º we avoid crustal triplications • At distances less than 80º we prevent effects from core diffraction

  6. 10 years (1997 - 2007) Mw=6.7+ 250+ earthquakes Global Catalog • 11,000+ recordings • avg. 45 rec/ event • E determined in f-domain

  7. Global catalog results • Global average for θ= -4.5 • Slow Tsunami earthquakes show a value of <-5.7

  8. Location of a big TsE (Nicaragua 1992) 50 events from 1981 to 1997 (Okal & Newman, 2001) 38 events of Mw > 5.7 from 1997 depth less than 70 km. θ= -5.1 no along-strike or down-dip trends are apparent. events may rupture more slowly, or more generally, with a lower stress drop than the global average. Central America

  9. We can obtain estimations for Tr from radiated energy at high frequencies (0.5-2Hz) Kuril Islands 13/01/2007 Mw=8.2 Rupture durations (Tr) Sumatra 26/12/2004 Mw=9.0 TsE: Java 17/07/2006 Mw=7.7

  10. Helps to differentiate Tsunami earthquakes, characterized for having long ruptures, Tr, and reduced energy, E Strong Earthquakes Tsunami earthquakes Rupture durations and Energy

  11. Summary and Conclusions • We have a robust dataset of 10yrs of earthquakes with estimated released energy, E/M0 • Global average of θ is -4.5 • TsE identifiable for being energy deficient <-5.7 • Central America regional studies: • Show E/M0 averages lower than the global average: could mean overall slower ruptures or local lower stress drop • Its possible to obtain rupture times from HF calculations in near real time due to speed of calculations • Further discrimination of tsunami earthquake

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