Earthquakes and Faulting

Transcription

1 Earthquakes and Faulting Crustal Strength Profile Quakes happen in the strong, brittle layers Great San Francisco Earthquake April 18, 1906, 5:12 AM Quake lasted about 60 seconds San Francisco was devastated by: Ground shaking Fires Most damaging earthquake in US history First quake studied in detail by geologist Lead to scientific understanding of quakes 1906 San Francisco San Francisco Burning Damage Dead- more than 3,000 Homeless- 225,000 Buildings destroyed- 28,000

2 Surface Rupture, Olema, CA Louis Agassiz (famous geologist) after the 1906 San Francisco earthquake. Stanford University Campus Fault Offset 2.5 m (8 ft) San Andreas fault at the Carrizo plain Recent rupture along San Andreas in Southern California

3 1906 Rupture- 430 km long Key Observations Earthquake was linked to a major fault A huge area was displaced horizontally Displacement was sudden Elastic Rebound Theory Crust is like a spring Deformation (strain) is stored as the fault-blocks move Eventually the fault fails Strain is released -> Quake Strain begins to accumulate again etc... ~3 meters Earthquake Cycle GPS position of Concepcion (Chile) IGS08 ref. frame Strain builds up until an earthquake releases it Size of quake depends on amount of strain stored Earthquakes are recurrent Small quakes are frequent Large quakes are rare Cycle may be 100s of years for large quakes 2010, Mag 8.8

4 Number of Quakes per year in Southern California Terminology Quakes per Year Focus- origin of rupture Epicenter- point at the surface above the focus Fault scarp- vertical offset at the surface Turcotte, 1992 Scarp, Alaska 1964 Seismic Waves Body waves P-wave (Primary Waves) S wave (Secondary Waves) Surface waves- most damaging Love waves Rayleigh waves Primary waves P-waves Particles move in same direction as wave propagation Pressure waves Like sound Fastest

5 Secondary Waves S-waves Particles move perpendicular to wave direction Shear Waves Cannot pass through liquids Slower than P-waves Seismic Record Focal mechanism Southern Alaska Focal Mechanisms Lower Hemisphere Stereographic projection Effects of earthquakes Turkey Ground motion Structural collapse Fire Landslides Liquefaction Permanent displacement of land surface Tsunamis Anatolian Earthquake- Turkey 1999

6 Earthquake damage Nigata Japan, Solifluction Nigata, Japan 1964 Earthquake-safe buildings tipped over, but did not collapse Quake Triggered Landslide El Salvador Coseismic Deformation in from Sept M quake in Canterbury, New Zealand Denali Fault, Alaska 2003 Quakes

7 Slides Triggered by Denali fault Quake 2003 GPS Velocity Field Velocity Relative to North America Hector Mine Quake 1999 M=7.0 Fault Map UNAVCO, 2015 Mohave Desert 0.3 sec Hector Mine

8 1 sec Hector Mine 3 sec Hector Mine Radar Interferometry (INSAR) Vertical Displacement Field Hector Mine Quake interferogram from Synthetic Aperture Radar data. Each fringe is 28 mm of vertical displacement. Hector Mine fault Landers fault D.T. Sandwell, EOS 11/11/03 Hector Mine Focal Mechanism Shaking during Loma Prieta Quake, 1989

9 Earthquakes prediction Sequential Ruptures of the Anatolian Fault Scientific techniques being explored Patterns of earthquakes in space & time Microseisms Surface tilts & changes of elevation (Strain accumulation) Shake probability in the next 50 years Earthquake Magnitude- Frequency Relationship period Kanamori and Brodsky, 2001 San Francisco Bay San Francisco Bay San Andreas Fault

10 San Andreas Fault Risk San Francisco Bay Area Earthquake Size and Frequency USGS Earthquake Hazard Map, Tectonic Quakes Only 2016 USGS Earthquake Hazard Map, Including Man-Made Quakes New Madrid Seismic Zone Brown Green- before 74 Can Quakes Occur in West Virginia? World Stress Map, 2005