Lecture 30

Lecture 30 - Indonesian Earthquake and Tsunami Number of...

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Unformatted text preview: Indonesian Earthquake and Tsunami Number of deaths and missing shown in ovals 12.00.a1 Indonesian Earthquake and Tsunami Before tsunami After tsunami Destruction of Destruction Banda Aceh Banda 12.00.a Describing Earthquakes Seismic waves Seismic radiate outward from hypocenter from Epicenter Epicenter Hypocenter Seismic Seismic stations: wave arrives at closer seismic stations first stations What causes most earthquakes? Normal faults Reverse and Reverse thrust faults thrust Strike-slip faults 12.01.a How could volcanoes generate seismic waves? Explosive eruption Movement Movement along faults along 12.01.c Slope failure Movement of Movement magma magma What else can cause seismic waves? Meteoroid impacts Landslides Explosions Before, During, and After an Earthquake Slip and Slip earthquake earthquake Stress Stress increase and elastic strain increase Post-slip recovery Post-slip of elastic strain; cycle starts again cycle 12.02.a Observe how earthquake ruptures grow Starts as small Starts patch below surface patch Borah Peak scarp Migrates out, Migrates ruptures surface (fault scarp) (fault Fault scarp Fault lengthens lengthens Landers scarp 12.02.b Observe where earthquakes occur Europe Europe Asia North North America America Africa Subduction Subduction zones zones South South America America Interior of Interior some continents continents Australia Other plate Other boundaries boundaries 12.03.a1 yellow - shallow; green - intermediate; red - deep Earthquakes Along Mid-Ocean Ridges Observe the types of activity that occur along mid-ocean ridges Faulting Faulting near rift near Mid-ocean ridge ridge Transform fault Faulting on Faulting transforms transforms Oceanic crust Lithospheric mantle Asthenosphere Injection of magma 12.03.b How Subduction Causes Earthquakes Trench and prism 12.03.c Volcanoes Thrusts South South America America Su bd uc tin g Continental crust pl at e Plate boundary Plate (megathrust) (megathrust) Lithospheric Lithospheric mantle mantle Ast hen osp her e Deep slab Thrusts How could How continental collisions cause earthquakes? earthquakes? Underthrusting plate Faults in Faults interior interior Overriding plate Plate Plate boundary boundary Transform Transform fault fault How could How earthquakes be generated within continents? continents? Continental Continental rift rift Continental crust crust Lithospheric Lithospheric mantle mantle Asthenosphere Faults in Faults interior interior Magma 12.03.d-e Different Kinds of Seismic Waves Surface waves Vertical surface wave compresses materials Horizontal Horizontal surface wave shears material shears Primary body Primary wave (P-wave) compresses material; fastest material; Body waves Secondary body Secondary wave (S-wave) shears material shears 12.04.a How Seismic Waves Are Recorded Modern Modern seismometer seismometer Basic Basic seismometer seismometer Waves on seismogram Seismogram 12.04.b-c How do we determine the location of an earthquake? Earthquake recorded by Earthquake seismic network seismic Select earthquake records 12.05.a Estimate distance Triangulate the epicenter Measuring the Size of an Earthquake For local magnitude For (Richter): Measure S-wave amplitude S-wave Connect amplitude and distance on plot and There are other ways we measure There the size of an earthquake 12.05.b Predict what destruction arises from Loma Prieta Predict Aftershocks Aftershocks ground motion during an cause further earthquake earthquake damage damage Rupture Landslide Structural Structural damage damage Tsunami Bridge failure Bridge on weak materials materials Liquefaction Liquefaction of fill of Worse if poor Worse construction construction Loma Prieta 12.06.a Destruction that Can Happen After an Earthquake Fire Tsunami and other flooding Limiting Risk from Earthquakes Improve Improve building design (engineer for earthquake) earthquake) 12.06.b-c Produce Produce and use hazard maps maps Major North American Earthquakes New Madrid, New 1811-1812 1811-1812 12.07.a Alaska, 1964 Hebgen Lake, 1959 San Francisco, 1906 Northridge, 1994 Mexico City, 1985 Charleston, 1886 Major World Earthquakes Nicaragua, 1972 Japan, 1999 Armenia, 1988 12.08.a Chile, 1960 Turkey, 1999 Taiwan, 2004 How Does a Tsunami Form? Waves radiate Waves away from fault away Higher waves Higher near shore near Most from faults on Most seafloor seafloor Waves Waves inundate land inundate 12.09a Fault movement Fault on ocean floor on Underwater landslides Underwater Volcanic eruptions Destruction by Destruction Tsunamis Tsunamis 12.09.b Chile, 1960 Hawaii, 1960 Japan, 1993 New Guinea, 1998 Studying Earthquakes in the Field Study main Study rupture rupture Measure small cracks and faults Measure to infer movement and stress to Offset of features Offset and evidence of past movement past Document changes Document in topography in 12.10.a1 Studying Faults with Satellites and Maps Map of geologic Map materials (yellow is recent sediment) recent Estimated ground Estimated accelerations (red is high) is Ground displacement Ground from repeated satellite measurements measurements 12.10.b Studying the Anatolian Fault, Turkey Detailed topographic profile across scarp Map of trench wall with C-14 Map dates dates 12.10.c Studying the San Andreas Fault Drilled into fault at Drilled depth to investigate rocks and conditions and Studies of shallow Studies trenches to document history document 12.10.m1 What areas are most likely to experience earthquakes? Near plate boundaries Messy collision zones Subduction zones Continental rifts 12.11.a What areas in the U.S. are most What likely to experience earthquakes? likely Alaska subduction zone Cascade subduction zone San San Andreas and related faults faults Intermountain Intermountain seismic belt seismic Hawaii Hawaii Big Island Island New Madrid area 12.11.a Long-Range Earthquake Forecasting Top graph indicates earthquakes prior to October, 1989; Top gaps identified based on less earthquake activity gaps 1989 earthquake filled 1989 in Loma Prieta gap in 2004 Parkfield earthquake 2004 filled in other gap filled 12.11.b When will San Francisco gap be filled? Long-Range Earthquake Forecasting USGS assigned USGS probability to each main fault in San Francisco area Francisco Combined probability Combined of major earthquake before 2032 is over 60 percent! percent! 12.11.b Short-Term Earthquake Prediction Lasers monitor Lasers movement along fault movement Numerous seismic Numerous instruments instruments EQ EQ did not occur exactly when predicted predicted 12.11.c Predictions based on past Predictions history of Parkfield segment history Red: Red: segment ruptured 1906 S.F. earthquake earthquake What Is the Earthquake What History of the San Andreas Fault and Related Faults? Fault Black and colored lines: Black recently active faults recently Blue: creeping Blue: segment segment Parkfield segment (north Parkfield end of orange) ruptures every ~20 years every Orange: last fully ruptured in Orange: 1857 (“Big One” for L.A.) 1857 Moderate EQs Moderate along eastern zone zone 12.12.a1 Observe features along the San Andreas fault 12.12.a Aerial photograph Aerial of same area of Exploring the Subsurface: Physical Samples Exposures of deep, Exposures uplifted rocks Magma that Magma brings up pieces of deeper rocks Mines Mines Drilling 12.13.a Exploring the Subsurface: Geophysical Surveys 12.13.a Electrical surveys Magnetic data Seismic-reflection data Gravity Gravity model model Gravity Gravity data data How Seismic Waves Travel Through Material 12.14.a Seismic wave radiates in Seismic all directions all At a boundary, wave At will reflect or refract will From faster to From slower material slower From slower to From faster material faster Rising wave from Rising faster to slower faster A seismic seismic wave bends as it travel through crust and mantle and 12.14.b Curved paths permit us to find depth to crust-mantle Curved boundary (Moho) boundary Close to EQ, paths Close through crust arrive first through Farther, paths through Farther, faster mantle arrive first faster Examine the ray Examine paths of seismic waves through Earth waves Size of core Size indicated by location of Plocation wave shadow wave zone zone S-waves do S-waves not pass through outer core (so liquid) core 12.14.c Investigating Deep Processes Study rocks with deep origins Use computers Use to model processes processes 12.15.a Replicate deep Replicate conditions in a laboratory conditions Seismic Tomography: Exploring Earth’s Interior Seismic Seismic observations from different direction direction Granite Sedimentary Sedimentary rocks rocks Interpretation Interpretation by comparing observed with what was expected if all same material same Average Average material material Slow material Fast Fast material material 12.15.b Seismic Velocities of the Lowermost Mantle Seismic Vary from Place to Place Vary Velocities Velocities (red = slow) (red Model to explain Model velocities velocities 12.15.c Great Alaskan Earthquake of 1964 Sliding along clay Landslides Shaking and sinking 12.16.a Manifestations of the Earthquake in the Sea Fa ul t Fault Fault Tsunami destroys coastal areas Seafloor uplifted 4 to 5 m Seafloor along faults along 12.16.b How Geologists Studied the Earthquake Mapped areas uplifted and Mapped subsided by earthquake subsided Generalized map of area Generalized cross Generalized section of megathrust section 12.16.c Investigation: Where Did This Investigation: Earthquake Occur, and What Damage Might Be Expected? Damage 12.17.a Seismograms DistanceTime Time Graph Graph ...
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This note was uploaded on 01/24/2011 for the course GEOL 100 taught by Professor Martin during the Fall '08 term at Maryland.

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