1 / 47

Introduction to seismology

Introduction to seismology. Mathilde B. Sørensen and Jens Havskov. Course content. Introduction: Eartquakes and seismicity Seismic rays and Earth structure Instruments and networks Seismic phases and location of earthquakes Magnitude Fault plane solutions Seismotectonics Tsunamis

mrenz
Download Presentation

Introduction to seismology

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Introduction to seismology Mathilde B. Sørensen and Jens Havskov

  2. Course content • Introduction: Eartquakes and seismicity • Seismic rays and Earth structure • Instruments and networks • Seismic phases and location of earthquakes • Magnitude • Fault plane solutions • Seismotectonics • Tsunamis • Volcano seismology • Hazard

  3. What is an earthquake?

  4. Shearer, 1999 Why study earthquakes ? Obtain earth structure

  5. Why study earthquakes? Understand tectonics

  6. M. Sørensen, 2008 M. Sørensen, 2008 Why study earthquakes? Mitigate effects from earthquake disasters

  7. Why study earthquakes:Tsunami warning March 11,2011

  8. Why study earthquakes: Warn of volcanic eruptions

  9. Earthquake and volcano locations Yellow dots are earthquakes and red triangles active volcanos

  10. Earthquakes in Norway NNSN1970 –2010

  11. Earthquakes in the Caribbean sSeismicity 1974-2013 from USGS Harbitz et al. 2012

  12. Deep seismicty used to discover subduction

  13. Seismicity of volcanos, Koryaksky

  14. Tectonic plates

  15. The seismic cycle An earthquake occur as a sudden release of strain which has built up at either side of the fault. The earthquake causes a permanent displacement across the fault.

  16. San Francisco, 1906

  17. Three types of plate boundaries

  18. Geometry of faults Faultgeometry is described by three parameters: Strike (directionofthefault) Dip (inclinationofthefault) Rake/slip (directionofrupture) Hangingwall Foot wall

  19. Fault types

  20. Normal fault

  21. Reverse fault

  22. Strike-slip fault Dekstral eller sinistral?

  23. Fault types Most earthquakes will be a mix of the three main types

  24. Earthquakeenergy travels through Earth as seismicwaves

  25. Types ofseismicwaves Body waves Surface waves Waves cause destruction Waves used to locate the earthquake and determine magnitude of the earthquake

  26. A simple seismometer Principle behind the inertial seismometer. The damping of the motion can be mechanical, but is usually electro-magnetic.

  27. Seismometers Seismometers register seismic waves arriving at the surface at seismic stations Nearby earthquake Distant earthquake

  28. Seismic wave velocity and global structure P-waves are faster than S-waves. Surface waves are slower than S-waves

  29. Local crustal structure

  30. Global crustal thickness

  31. Principle of fault plane solution First motion of P observed at different directions relative to the fault plane for a strike-slip fault. The 2 arrows in the fault plane show the relative slip direction in the fault plane. Figure modified from Stein and Wysession, 2003.

  32. Some fault plane solutions from seismology

  33. Earthquake location A seismogram

  34. Earthquake location The time difference between P- and S-waves will increase as the distance to the epicenter increases. We can therefore use the time difference to determine the distance between the earthquake and the station

  35. Earthquake location • 1 station: infinite amount of possible locations • 2 stations: two possible locations • 3 stations: one possible location Station 1 Station 2 Station 3

  36. How strongwastheearthquake • There are different measures for the strength of an earthquake • Some describe the rupture, other the effect on the surface of Earth • The most important for the general public is magnitude often referred to as the Richter magnitude

  37. Amplitude Magnitude determination Magnitude can be determined by measuring the amplitude of the seismic waves on a seismogram We must also take into account that shaking becomes weaker with increasing distance to the epicenter

  38. The Richter scale Magnitude must be corrected for distance to the epicenter

  39. General magnitude scale A: Maximum amplitude B: A constant R: Distance C: A constant

  40. Seismic moment M0 • Measure for the strength of an earthquake • Determined from the area of the rupture and the displacement during the earthquake: M0  area • Can be used to calculate the most accurate magnitude

  41. Earthquake effects, what controls the damage? • Amplitude of the seismic waves • Magnitude • Distance • Local geology • Frequency content of ground shaking • Building quality • Indirect damages (secondary effects) • Fire • Landslide/rock fall • Tsunami • Liquefaction

  42. Building quality

  43. Frequency content

  44. Seismic hazard in California

  45. Actual shaking during an earthquake

  46. Volcano hazard example from Colombia

  47. Conclusion Seismology is much more then earthquake studies Seismology is useful to study in many fields of geoscince Seismology also essential in many prospection methods seismology

More Related