Earthquakes

1. Earthquakes

2. Solid Earth Seismology Theory, Practice, and Application to the Earth's Interior GEOL 595 SP/L Text Book: Introduction to Seismology By Peter M. Shearer

3. What is Seismology ? • From the Greek root word: “seismos” to shake • Seismic Waves: elastic wave energy that propagates in solid or fluid materials. • Seismology: the study of earthquakes and the elastic waves generated by the rupture.

4. What is Seismology ? • Seismic Waves: elastic wave energy that propagates in solid or fluid materials. - energycreation (earthquakes, nukes, bombs, eruptions, sonic booms) - energytransmission (propagation, absorption, scattering, reflection, diffraction) - energyrecording (seismometry, computer storage, data transmission, etc) - societal (e.g., forecasting earthquakes, seismic)

5. What is Seismology ? Seismology bridges: Geology + Geophysics + Earth Science • Seismic imaging at depth can verify whether geological observations (e.g. faults, plate boundaries,ancient sutures, granitic outcrops) on the surface continue to deeper depths in the crust or mantle. • Earthquake aftershocks can help us map faults and plate boundaries at depth in the crust and mantle. • Measurements of seismic anisotropy can indicate whether mineralogical alignment occurs during plate movement or shear. • Volcano seismology measure earthquake patterns that may indicate magma rising through a volcano chamber

6. Mount St Helen's movie * Erupted 1980, Washington State * Local earthquakes felt 2 months before * Evacuations saved 1000's of people * 57 people died including Inn keeper Harry Truman, a photographer, a geologist, and many animals.

7. Earthquakes can tell us about Magma Flow beneath Volcanoes - An eruption event at Mt St Helen's in September, 2005 - Can be seen in the earthquake record by deep events of magma flow

8. Magnitude 9.0 NEAR THE EAST COAST OF HONSHU, JAPANFriday, March 11, 2011 at 05:46:23 UTC The map on the right shows historic earthquake activity near the epicenter (star) from 1990 to present. As shown on the cross section, earthquakes are shallow (orange dots) at the Japan Trench and increase to 300 km depth (blue dots) towards the west as the Pacific Plate dives deeper beneath Japan. Seismicity Cross Section across the subduction zone showing the relationship between color and earthquake depth. Images courtesy of the US Geological Survey

9. Northridge Earthquake, 1994 San Fernando, 1971 San Fernando, 1971 Northridge, 1994 Seismic image of a blind thrust fault at depth

10. Seismology and Society Study of Seismology, seismic waves, and earthquakes Also aid in hazard analysis for communities in earthquake country. - Earthquake risk - Earthquake Engineering - Tsunami hazard analysis

11. CSUN Parking Structure Northridge Earthquake, 1994 - January 17, 1994, 4:30 am - Magnitude = 6.9 - Blind thrust fault - Difficult to find or predict - Duration 10-20 seconds

12. Northridge Earthquake, 1994 * CSUN Parking Structure (near G3 and G4 parking lot today)‏ * Built in 1991, three years before the earthquake.

13. Northridge Earthquake, 1994 Earthquake damage to freeways, buildings, cars, gas lines.

14. Magnitude 9.0 NEAR THE EAST COAST OF HONSHU, JAPANFriday, March 11, 2011 at 05:46:23 UTC This tsunami propagation forecast model shows the forecast maximum tsunami wave height (in cm). Ocean floor bathymetry affects the wave height because a tsunami moves the seawater all the way to the floor of the ocean. This led to a Pacific wide tsunami warning being issued.

15. Magnitude 9.0 NEAR THE EAST COAST OF HONSHU, JAPANFriday, March 11, 2011 at 05:46:23 UTC Projected travel times for the arrival of the tsunami waves across the Pacific. Nearby the earthquake there are only minutes to evacuate. However, in many other regions there is advance warning. A tsunami map shows projected travel times for the Pacific Ocean. This map indicates forecasted times only, not that a wave traveling those distances has actually been observed.. NOAA

16. Magnitude 7.3 Earthquake near Elsalvador Sunday night ! • Earthquake Mg 7.3 (Aug 26, 2012) • Offshore Elsalvador (9:30 pm California time) • Tsunami warning was put into effect for Costa Rica, Nicaragua, • El Salvador, Honduras, Guatemala, Panama and Mexico.

17. The underlying physics is simple: F = ma Force, V = d / t Velocity, What is Seismology ? But assumptions can quickly become complex when considering realistic sources, Earth structure that changes with depth and pressure, and receiver instrumentation. Requires more sophisticated math and computation.

18. Early Detectors of Ground Movement Zhang Heng was a celebrated astronomer of ancient China. An inventor of the seismoscope and armillary sphere, he made great contributions to the development of astronomy in ancient China. 132 AD, Eastern Han Dynasty

19. Seismology and Plate Tectonics • Earthquakes generally occur at plate boundaries. • Thus plate tectonics is intimately linked with earthquakes and seismology

20. Seismology and Plate Tectonics Most of the largest earthquakes occur at collisional plate boundaries.

21. Planetary Seismology ? • What kind of living would a seismologist make on another planet ? • What is the plausibility of earthquakes on other planets, on the moon ? - Is there active plate tectonics on other planets ?

22. Seismic waves inside the Earth How does earthquake energy travel through the Earth's interior ?

23. Movie: Wysession

24. Seismic Tomography: from Seismic rays in the Earth • Many seismic stations placed across a region of interest • Create Images of “velocity” or seismic structure

25. Earth's Interior Structure Seismology is the chief method of determining the interior Structure of the Earth. Indirect methods of studying the Earth's Interior

26. Can we just go to the center of the Earth ? • Deep interior of the Earth must be studied indirectly • Direct access only to crustal rocks and small upper mantle fragments brought up by volcanic eruptions or slapped onto continents by subducting oceanic plates • Deepest drill hole reached about 12 km, but did not reach the mantle • Geophysics is the branch of geology that studies the interior of the Earth SE Germany – 10 km drill hole

27. Indirect Study of the Earth's Interior - Geophysics - Seismic Waves - Gravity - Heat Flow - Magnetic Field

28. The Mantle Lithosphere • Crust and upper mantle together form the lithosphere, the brittle outer shell of the Earth that makes up the tectonic plates • Lithosphere averages 70 km thick beneath oceans and 125-250 km thick beneath continents

29. The Asthenosphere • Beneath the lithosphere, seismic wave speeds abruptly decrease in a plastic (ductile) low-velocity zone called the asthenosphere • Are low seismic velocities caused by partial melt, water, density?

30. Subduction Zones in North America • Subducting Farallon slab is imaged through seismic tomography extending to at least 2000 km depth • Farallon reaches this depth somewhere beyond the east coast of North America • Grand et al., 2001.

31. Earth's resources Oil exploration Active source Reflection seismology Gasoline contamination Environmental compliance

32. Petroleum Recovery • Oil fields are regions underlain by one or more oil pools • Largest in U.S. are in Texas and Alaska • Oil and natural gas are removed through wells drilled down into an oil trap within a reservoir rock • Negative environmental effects resulting from oil recovery and transport include oil spills, brine contamination of surface water, and ground subsidence

33. Exploration Geophysics

34. Exploration Geophysics: Metals and Ores • Metal ores - naturally occurring materials that can be profitably mined • Whether or not a mineral deposit is an ore depends on chemical composition, the percent extractable metal, and current market value of the metal • Metallic ore deposits originate from crystal settling in igneous intrusions, hydrothermal fluids cooling in pores and factures, chemical precipitation in water, or sedimentation in rivers (placers)

35. Exploration Geophysics: Mining metals • Mining can be done at Earth’s surface (strip mines, open-pit mines, and placer mines) or underground • Metals mined include iron, copper, aluminum, lead, zinc, silver, gold and many others • With care, negative environmental effects of mining, including unsightly tailings piles, surface scars, land subsidence, and acid mine drainage can be minimized

36. Earthquake Source Theory Quantification of the earthquake rupture process

37. Earthquakes

38. Seismogram A seismogram is made up of a series of signals only one of which is the earthquake. • Earthquake source • Scalar • Explosion • Rupture along a plane (e.g. shear) • Receiver characteristics • Medium wave travels through Diagram....SW...figure.

39. Seismology: What is Known an Unknown What we know for sure! - Vp speed (fraction of a percent) - Average radial velocity of Earth Know very well fo 50 years! - Earthquake locations Mapped daily y GSN - EQ radiation patterns “ What we are still studying: - Physics of earthquake rupture largely unknown. - Damping by inner core Only approximate

40. CSUN Parking Structure Northridge Earthquake, 1994 - January 17, 1994, 4:30 am - Magnitude = 6.9 - Blind thrust fault - Difficult to find or predict - Duration 10-20 seconds

41. Northridge Earthquake, 1994 * CSUN Parking Structure (near G3 and G4 parking lot today)‏ * Built in 1991, three years before the earthquake.

42. Northridge Earthquake, 1994 Damage to freeways, buildings, cars, gas lines.

43. Historic Earthquakes 1994 Northridge - 1.8 miles from CSUN - Shaking 40 seconds - Damaged all 53 CSUN buildings - Damaged 300 other schools - Lower story buildings collapsed - 4 interstate hwy's closed for months (Golden State, Santa Monica fwys) - 15000 people live in tents for days - 10000 without water, elect, gas - Arid climate did not cause liquifaction of soils – shaking minimized (compared to 1964 Alaska and 1989 Loma Prieta). - Landslides in Santa Susana, Santa Monica, San Gabriel Mtns blocked roads and traffic, damaged water lines and homes in Palisades - Sylmar – Olive View Hospital – rebuilt from 1971 to code stayed intact. - Aftershocks 5.9 1 min after main shock, 5.6 11 hrs after.

44. Earthquakes 1989, Loma Prieta earthquake, Mw = 7.2

45. Historic Earthquakes 1906 San Francisco - 280 miles of displacement - Shaking ~1 minute - Damaged water mains, fires spread and caused many deaths (3000).

46. Historic Earthquakes 1989 Loma Prieta, Mw = 7.2 - Shaking for 15 seconds - Death toll 63

47. Historic Earthquakes 1964 southern Alaska (Mw = 9.2)‏ - Shaking for 3 minutes - Rupture 350,000 square miles - Death toll from quake 15 (remote area)‏ - Tsunami, landslides 100 more

48. Historic Earthquakes 2002 inland Alaska – Denali Fault - Propagated east 7000 miles/hr - Offset streams, glaciers, landslides - Trans-Alaska Oil Pipeline no serious damaged - pre-engineered

49. Historic Earthquakes 2004 Sumatra – Andaman E.Q. - Mw = 9.3 - Second largest recorded on Earth - Major damage in Sumatra - Tsunami damage spread far to Indonesia, Thailand, Sri Lanka, India, East Africa - Death toll 220,000 from force of tsunami wave - Tsunami movie