Estimating the frequency, magnitude and recurrence of extreme earthquakes in medina area, Saudi Arabia

Humans coexist with extreme events all the time, only when the intensity of the event becomes greater than a certain level there is a resulting disaster. Small earthquakes occur all of the time with no adverse effects. Only large earthquakes cause disasters. Statistical analysis reveals that larger events occur less frequently than small events. In a year, we would have many values for the events; the annual maximum is the greatest of those values. Within an annual series, only the largest value per year is allowed, even if an additional significant peak occurred. As the magnitude of a hazardous increases, the frequency of occurrence (how often a given magnitude is equaled or exceeded) decreases. Thus, major disasters result from a small number of large events that rarely occur. A plot of recurrence intervals versus associated magnitudes produces a group of points that also approximates a straight line on semi-logarithmic paper. Historical data are analyzed to gain an understanding of an event past behavior and to provide guidance on expected future. The extreme event analysis is concerned with the distribution of annual maximum values at a given site. These events are given a rank in a descending order. The Weibull equation is used for estimating the annual frequency, the return period or recurrence interval, the percentage probability for each event, and the annual exceedence probability. The probability of a certain-magnitude earthquake occurring in the region during any period can be also calculated. Past records of earthquakes at the Western region of the Kingdom of Saudi Arabia (Medina and surrounding area) for years 1921 G- 2010G are used to predict future conditions concerning the annual frequency, the return period, the percentage probability for each event, and the probability of a certain-magnitude earthquake occurring in the region during any period.