ÖNCEL AKADEMİ: INTRODUCTION TO SEISMOLOGY

Department of Earth Sciences KFUPM Introduction to Seismology Earthquake Statistics (pp. 371-396) Introduction to Seismology-KFUPM Ali Oncel [email_address]

Term-Paper Status Deadline: May 3 First Draft: Through the e-mail Introduction to Seismology-KFUPM

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

Recall: Homework due March, 28 ,[object Object],[object Object],[object Object],Introduction to Seismology-KFUPM

Previous Lecture ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Introduction to Seismology-KFUPM

MAGNITUDE OCCURRENCE ,[object Object],log 10 N c (m) = a - bm ,[object Object],[object Object],m 1 = a/b [i.e. N c = 1] Introduction to Seismology-KFUPM

Difficulties in practise ,[object Object],[object Object],[object Object],[object Object],[object Object],Introduction to Seismology-KFUPM

EARTHQUAKE OCCURRENCE ,[object Object],[object Object],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

P(T) =  e -  T ,[object Object],[object Object],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)

IMPLICATIONS ARE: ,[object Object],[object Object], 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

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

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

ÖNCEL AKADEMİ: INTRODUCTION TO SEISMOLOGY

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ÖNCEL AKADEMİ: INTRODUCTION TO SEISMOLOGY