Earthquake Prediction Accurate prediction of earthquakes is not currently possible, although intensive research is proceeding in many areas. Two types of earthquake prediction are theoretically possible. The first type is long-term forecasting, in which the probability of an earthquake along a particular segment of a within a certain time interval is calculated by studying seismic gaps and historical records of earthquakes that have occurred along that fault segment. By plotting the number of earthquakes within specific time intervals against their magnitudes, diagrams can be constructed for a local area. From this plot it is possible to determine the recurrence interval, or the average time interval between earthquakes of a specific magnitude. Predictions can then be made that an earthquake of that magnitude has a high probability of occurrence within a specified time interval if the date of the last earthquake is known. 1. According to paragraph 2, all of the following information is used in the process of long-term earthquake prediction EXCEPT the A. analysis of seismic gaps B. record of past earthquakes in the fault area C. date of the last recorded earthquake in the area D. pattern of earthquake activity in other nearby fault segments 2. According to paragraph 2, long-term forecasting can be used to predict which of the following A. The influence of earthquake activity in one segment of the fault area on other segments B. The frequency with which earthquakes of a certain size will occur C. The possible date of the next earthquake D. The magnitude of the next earthquake Research leading to short-term forecasting, which involves a shorter time interval, has been focused on precursors observed prior to previous earthquakes. Precursors are physical or chemical phenomena that occur in a typical pattern before an earthquake. These phenomena include changes in the velocity of seismic waves, the electrical resistance of rocks, the frequency of the usually minor preliminary earthquakes (foreshocks), the deformation of the land surface, and the water level or water chemistry of wells in the area. Many of these precursors can be explained by a theory called the dilatancy model. Under this hypothesis, rocks in the process of strain along a fault show significant dilation or swelling before rupture. This volume increase is caused by the opening of microcracks, which are minute failure zones in weaker mineral grains in the rock and along grain boundaries. Groundwater flows into the highly stressed areas during the formation of microcracks. These changes in density and water content affect the ability of the rock to transmit seismic waves and conduct electricity. Therefore, seismic-wave velocity and electrical resistance progressively change as the overall rupture along the fault draws near. Localized changes in land-surface elevation are a...
