ÖNCEL AKADEMİ: INTRODUCTION TO SEISMOLOGY
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The document discusses concepts related to earthquake statistics and analysis including: 1) Determining an earthquake's location by measuring seismic wave speeds and its magnitude by measuring ground shaking. 2) The Gutenberg-Richter frequency-magnitude relationship which finds that the number of earthquakes decreases exponentially with magnitude. 3) Challenges in applying this relationship including non-linearity at large magnitudes, largest earthquake events, and roll-off at lower magnitudes.
![Department of Earth Sciences KFUPM Introduction to Seismology Earthquake Statistics (pp. 371-396) Introduction to Seismology-KFUPM Ali Oncel [email_address]](https://image.slidesharecdn.com/lecture12-091219190226-phpapp02/85/ONCEL-AKADEMI-INTRODUCTION-TO-SEISMOLOGY-1-320.jpg)
![MAGNITUDE OCCURRENCE The Gutenberg and Richter (1944) cumulative frequency-magnitude law. The number of earthquakes in a region decreases exponentially with magnitude or : log 10 N c (m) = a - bm This is a whole process distribution , that means we use all the earthquakes in the data set or catalogue ( not aftershocks) The magnitude of the quake expected to be largest in a year is : m 1 = a/b [i.e. N c = 1] Introduction to Seismology-KFUPM](https://image.slidesharecdn.com/lecture12-091219190226-phpapp02/85/ONCEL-AKADEMI-INTRODUCTION-TO-SEISMOLOGY-6-320.jpg)
![P(T) = e - T or the distribution of time intervals T between quakes: Assumptions are: Introduction to Seismology-KFUPM The probability of a quake is identical for any interval along the time axis Stationarity (the mean rate is not a function of time) iii) L im P {[N (t, t + t)] > 1} = 0 t 0 Orderly events (probability of simultaneous events is zero) ii) N(t, t + ) independent of N ( , + ) Independent events i)](https://image.slidesharecdn.com/lecture12-091219190226-phpapp02/85/ONCEL-AKADEMI-INTRODUCTION-TO-SEISMOLOGY-9-320.jpg)
![IMPLICATIONS ARE: The interval T may be measured starting anywhere. An interval T of 10 years from the last quake is exactly as likely as an interval of 10 years from now (independence + stationarity). However, not all intervals T are equally likely. short intervals more likely than long ones. Events appear to cluster - pseudo-clustering. Earthquakes are not uniformly spaced in time. corollary : uniformly spaced earthquakes in time implies a highly organised, non-random controlling process. [consider the traffic analogy] [consider apparent changes in seismicity] Introduction to Seismology-KFUPM](https://image.slidesharecdn.com/lecture12-091219190226-phpapp02/85/ONCEL-AKADEMI-INTRODUCTION-TO-SEISMOLOGY-10-320.jpg)
ÖNCEL AKADEMİ: INTRODUCTION TO SEISMOLOGY
- 1. Department of Earth Sciences KFUPM Introduction to Seismology Earthquake Statistics (pp. 371-396) Introduction to Seismology-KFUPM Ali Oncel [email_address]
- 2. Term-Paper Status Deadline: May 3 First Draft: Through the e-mail Introduction to Seismology-KFUPM
- 3. You have learned how to pinpoint the location of an earthquake by measuring the speed of seismic waves radiating away from the focus of the earthquake . Now, we can determine an earthquake's magnitude by measuring the strength of ground shaking as you did for global earthquakes . Learn how to do both these things by visiting the virtual earthquake web page. http://www.sciencecourseware.org/VirtualEarthquake/VQuakeExecute.html and completing the exercise . It should take you about 30 minutes . Turn in your certificate of completion at the beginning of class on Monday, 26 March. Homework: VIRTUAL SEISMOLOGY Introduction to Seismology-KFUPM
- 4. Recall: Homework due March, 28 Through the Interactive Data Module which is explained so far http://atlas.geo.cornell.edu/ima.html Prepare the focal mechanism map of the area for your term project as file *.jpg, send it to me via e-mail due next lecture. Also, try to provide a discussion about one paragraph on types of the faulting deformation through the region. Introduction to Seismology-KFUPM
- 5. Previous Lecture Interactive Mapping Tool of Cornell University Interactive Mapping and Data Analysis Learn how to select Regional data of focal mechanism What is CMT? global Seismotectonic zones and their relation to earthquake depths seismicity patterns through the Continental Margins Seismicity through the plates of convergent and divergent Example: Mid-Ocean Ridge System and Transform Plate Boundary Seismicity through the Trunscurrent Fault Seismicity through the Transform fault Recommended Site for Fault Plane Solutions Introduction to Seismology-KFUPM
- 6. MAGNITUDE OCCURRENCE The Gutenberg and Richter (1944) cumulative frequency-magnitude law. The number of earthquakes in a region decreases exponentially with magnitude or : log 10 N c (m) = a - bm This is a whole process distribution , that means we use all the earthquakes in the data set or catalogue ( not aftershocks) The magnitude of the quake expected to be largest in a year is : m 1 = a/b [i.e. N c = 1] Introduction to Seismology-KFUPM
- 7. Difficulties in practise Often observe non-linearity or roll-off at large magnitude. (2) Largest earthquake “catastrophe”. (3) Often observe roll-off at lower magnitudes. Why (1), (2) and (3)? Reasons? Introduction to Seismology-KFUPM
- 8. EARTHQUAKE OCCURRENCE Simple Poisson process or random model: Assume that an earthquake or event in a given magnitude range and a given volume of the Earth’s crust is assumed to be found equally in any unit time interval, and it is independent of any other earthquake. P (n, t) = e - t Probability Density n: number events in time t if : the mean rate of occurrence Then, Poissonian probability : Introduction to Seismology-KFUPM
- 9. P(T) = e - T or the distribution of time intervals T between quakes: Assumptions are: Introduction to Seismology-KFUPM The probability of a quake is identical for any interval along the time axis Stationarity (the mean rate is not a function of time) iii) L im P {[N (t, t + t)] > 1} = 0 t 0 Orderly events (probability of simultaneous events is zero) ii) N(t, t + ) independent of N ( , + ) Independent events i)
- 10. IMPLICATIONS ARE: The interval T may be measured starting anywhere. An interval T of 10 years from the last quake is exactly as likely as an interval of 10 years from now (independence + stationarity). However, not all intervals T are equally likely. short intervals more likely than long ones. Events appear to cluster - pseudo-clustering. Earthquakes are not uniformly spaced in time. corollary : uniformly spaced earthquakes in time implies a highly organised, non-random controlling process. [consider the traffic analogy] [consider apparent changes in seismicity] Introduction to Seismology-KFUPM
- 11. DESIRABLE PROPERTIES OF EARTHQUAKE CATALOGUES Homogeneity: if parameters are redetermined then uniform redetermination magnitudes determined uniformly or calibrated against each other intensity values on same scale all parameters to known accuracy, e.g. hypocentres Complete: ideally complete down to small magnitudes, but certainly of known completeness Duration: catalogue to cover a long time span, ideally greater than the largest return periods Source material: known and referenced if there are multiple sources for some earthquakes and parameters are not uniformly re-determined then a stated hierarchy of preferences amongst sources Computer readable: simple format Introduction to Seismology-KFUPM
- 12. COMPLETENESS Depends on data availability. The usual and obvious bias is against small shocks in the earlier years. During the instrumental era it is a function of network density and detection threshold. In the pre-instrumental era (historical) it is a function of population density, culture and survival rate of documents. Introduction to Seismology-KFUPM