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. Why study earthquakes ? Obtain earth structure Shearer, 1999

5. Why study earthquakes? Understand tectonics

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

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 NNSN 1970 –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 Fault geometry is described by three parameters: Strike (direction of the fault) Dip (inclination of the fault) Rake/slip (direction of rupture) Foot wall Hanging 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. Earthquake energy travels through Earth as seismic waves

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

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. 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 How strong was the earthquake

37. 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 Amplitude

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 M 0 Measure for the strength of an earthquake Determined from the area of the rupture and the displacement during the earthquake: M 0  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 Seismology is much more then earthquake studies Seismology is useful to study in many fields of geoscince Seismology also essential in many prospection methods