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# Earthquake Occurrence

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• ### Earthquake Occurrence

1. 1. Department of Earth Sciences KFUPM Introduction to Seismology Earthquake Occurrence 2 Introduction to Seismology-KFUPM Ali Oncel [email_address]
2. 2. Previous Lecture <ul><li>Magnitude Occurrence </li></ul><ul><li>The Gutenberg-Richter Law </li></ul><ul><li>Difficulties in practice due to Lack of seismicity Data </li></ul><ul><li>Earthquake occurrence: Poisson Process and Probability </li></ul><ul><li>Earthquake Catalogues:  Desirable Properties </li></ul><ul><ul><li>Homogeneity </li></ul></ul><ul><ul><li>Completeness </li></ul></ul><ul><ul><li>Duration </li></ul></ul><ul><ul><li>Source Material </li></ul></ul><ul><ul><li>Online Data </li></ul></ul>Introduction to Seismology-KFUPM
3. 3. Recall: MAGNITUDE OCCURRENCE <ul><li>The Gutenberg and Richter (1944) cumulative frequency-magnitude law. The number of earthquakes in a region decreases exponentially with magnitude or : </li></ul>log 10 N c (m>M) = a - bm <ul><li>This is a whole process distribution , that means we use all the earthquakes in the data set or catalogue ( not aftershocks) </li></ul><ul><li>The magnitude of the quake expected to be largest in a year is : </li></ul>m 1 = a/b [i.e. N c = 1] Introduction to Seismology-KFUPM b= β x log e log e=0.4343
4. 4. Seismicity of Stable Cratonic Cores (SCC) Fenton, Adams, Halchuk, 2006
5. 5. Earthquake catalogue completeness Introduction to Seismology-KFUPM
6. 6. Magnitude-Frequency (per 50.7 x 106 km 2 ) plot for the worldwide SCC seismicity data set Introduction to Seismology-KFUPM
7. 7. Stable Craton Introduction to Seismology-KFUPM log 10 N c (m) = 3.68 – 0.947 m Once a decade a M6.5
8. 8. Worldwide rates of stable cratonic core seismicity Introduction to Seismology-KFUPM
9. 9. Introduction to Seismology-KFUPM
10. 10. Introduction to Seismology-KFUPM
11. 11. Introduction to Seismology-KFUPM
12. 12. stable west east 2002 Plattsburgh NY
13. 13. stable west east Introduction to Seismology-KFUPM
14. 16. There are several online catalogs of earthquakes. In this exercise, you will need to access one of these. For earthquakes any place in the world, a good place to start is: http://wwwneic.cr.usgs.gov/neis/epic/epic.html A catalog of focal mechanisms (CMT Solutions) is at the Harvard seismology site: http://www.seismology.harvard.edu/ You will need to use an Excel spreadsheet to solve some of these problems. Homework on Earthquake Search due May, 3 <ul><li>How many earthquakes occurred for the Saudi Arabia and vicinity since 1973 </li></ul><ul><li>with magnitude 6.0 or larger. </li></ul><ul><li>with magnitude 5.0 or larger. </li></ul><ul><li>with magnitude 4.0 or larger. </li></ul>2. Present your data, giving the average number of earthquakes per year and establish Log N= a – b M . 3. By consulting the Harvard catalog of moment tensors, for the largest of the events in this region, infer the main tectonic process in this region. Explain the reasoning behind your response. Introduction to Seismology-KFUPM
15. 17. Quiz 4 <ul><li>Explain the physical meaning of above graph? </li></ul><ul><li>What you think might be a reason for observing roll-off at lower (3) and higher (1) magnitudes. </li></ul>Introduction to Seismology-KFUPM Log N
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