پنج شنبه 17/10/1388 - 10:2
Earthquake predictionAn earthquake prediction is a prediction that an earthquake of a specific magnitude will occur in a particular place at a particular time (or ranges thereof). Despite considerable research efforts by seismologists, scientifically reproducible predictions cannot yet be made to a specific hour, day, or month but for well-understood faults, seismic hazard assessment maps can estimate the probability that an earthquake of a given size will affect a given location over a certain number of years. Once an earthquake has already begun, early warning devices can provide a few seconds" warning before major shaking arrives at a given location. This technology takes advantage of the different speeds of propagation of the various types of vibrations produced. Aftershocks are also likely after a major quake, and are commonly planned for in earthquake disaster response protocols. Experts do advise general earthquake preparedness, especially in areas known to experience frequent or large quakes, to prevent injury, death, and property damage if a quake occurs with or without warning.Prediction techniques In the effort to predict earthquakes, people have tried to associate an impending earthquake with such varied phenomena as seismicity patterns, electromagnetic fields (Seismo-electromagnetics), ground movement, weather conditions and unusual clouds, radon or hydrogen gas content of soil or ground water, water level in wells, animal behavior, and the phases of the moon. Many pseudoscientific theories and predictions are made, which scientific practitioners find problematic. The natural randomness of earthquakes and frequent activity in certain areas can be used to make "predictions" which may generate unwarranted credibility. These generally leave certain details unspecified, increasing the probability that the vague prediction criteria will be met, and ignore quakes that were not predicted. Rudolf Falb"s "lunisolar flood theory" is a typical example from the late 19th century.Evaluation of prediction theoriesOfficial earthquake prediction evaluation councils have been established in California (the California Earthquake Prediction Evaluation Council) and the federal government in the United States (the National Earthquake Prediction Evaluation Council), but have yet to endorse any method of predicting quakes as reliable. Scientific evaluations of prediction claims look for the following elements in a claim:
Attribution to a plausible physical mechanism lends credibility, and suggests a means for future improvement. Reproducibility and statistical analysis are used to distinguish predictions which come true due to random chance (of which a certain number are expected) versus those that have more useful predictive capability, and to validate models of long-term probability. Such models are difficult to test or validate because large earthquakes are so rare, and because earthquake activity is naturally clustered in space and time. "Predictions" which are made only after the fact are common but generally discounted.RadonEmission of radon as a quake precursor was studied in the 1970s and 1980s, with no reliable results. It is still under study at NASA as of 2009.Further information: Radon#ScientificThe VAN methodVAN is a method of earthquake prediction proposed by Professors Varotsos, Alexopoulos and Nomicos in the 1980s; it was named after the researchers" initials. The method is based on the detection of "seismic electric signals" (SES) via a telemetric network of conductive metal rods inserted in the ground. The method stems from theoretical predictions by P. Varotsos, a solid-state physicist at the National and Capodistrian University of Athens. It is continually refined as to the manner of identifying SES from within the abundant electric noise the VAN sensors are picking up. Researchers have claimed to be able to predict earthquakes of magnitude larger than 5, within 100 km of epicentral location, within 0.7 units of magnitude and in a 2-hour to 11-day time windowForeshock predictionsForeshocks are medium-sized earthquakes that precede major quakes.An increase in foreshock activity (combined with purported indications like ground water levels and strange animal behavior) enabled the successful evacuation a million people one day before the February 4, 1975 M7.3 Haicheng earthquake by the China State Seismological Bureau.While 50% of major earthquakes are preceded by foreshocks, only about 5-10% of small earthquakes turn out to be foreshocks, leading to many false warnings. Pattern theoriesAccording to new research to be published by Prof. Shlomo Havlin, of Bar-Ilan University"s Department of Physics, earthquakes form patterns which can improve the ability to predict the timing of their recurrence. In November 2005 (November 11 issue) the journal Physical Review Letters, published by the American Physical Society, published an article by researchers from Israel and Germany that say that there is a way to predict when the next earthquake will hit.Prof. Shlomo Havlin"s from Bar-Ilan University in Israel, in collaboration with Prof. Armin Bunde, of the Justus-Liebig University in Giessen, Germany, and Bar-Ilan University graduate student Valerie Livina used the "scaling" approach from physics to develop a mathematical function to characterize earthquakes of a wide range of magnitudes in order to learn from smaller magnitude earthquakes about larger magnitude earthquakes. The team"s findings reveal that the recurrence of earthquakes is strongly dependent on the recurrence times of previous earthquakes.This memory effect not only provides a clue to understanding the observed clustering of earthquakes, but also suggests that delays in earthquake occurrences, as seen today in Tokyo and in San Francisco, are a natural phenomenon.FractoluminescenceMain article: Earthquake lightOne possible method for predicting earthquakes, although it has not yet been applied yet, is fractoluminescence. Before the 1995 Kobe earthquake in Japan, many people reported seeing flashes of red and blue light in the sky up to an hour before the earthquake. Studies at the Chugoku National Industrial Research Institute by Yoshizo Kawaguchi have shown that upon fracturing, silica releases red and blue light for a period of about 100 milliseconds. Kawaguchi attributed this to the relaxation of the free bonds and unstable oxygen atoms that are left when the silicon oxygen bonds have broken due to the stresses within the rock.
- A specific location or area
- A specific span of time
- A specific magnitude range
- A specific probability of occurrence