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Earthquake forecasting using earthquake catalogs “Since my first attachment to seismology, I have had a horror of predictions and of predictors. Journalists and the general public rush to any suggestion of earthquake prediction like hogs toward a full trough.” - Charles Richter (1977) Whoever wishes to foresee the future must consult the past; Turn to you partner and discuss this statement 1) What does it mean? 2) Provide an example where it applies 3) Could this statement connect to earthquakes? How? Earthquake Prediction vs. Earthquake Forecasting Earthquake Prediction = a short-term (hours to days) statement that an earthquake of a specified size will occur at a given location. Earthquake Forecast = a long term (years to decades) statement of the probability of an earthquake in a region (or the probability of one or more earthquakes in a region). IRIS Earthquake Browser - www.iris.edu >For Educators Looking for seismicity patterns Steps : • Select a region of the world that is of interest to you • Interrogate the EQ catalogue to determine the number of various sized events that occur in a 25 year period for your region. (Start at min 9.0 and use M 0.5 intervals) – Make a 3 column table of • Magnitude • total number of earthquakes greater than or equal to a specified magnitude • number/year • Plot this information on the graph provided (or use Excel) IRIS Earthquake Browser - www.iris.edu >For Educators Looking for seismicity patterns Steps : • Select a region of the world that is of interest to you • Interrogate the EQ catalogue to determine the number of various sized events that occur in a 25 year period for your region. (Start at min 9.0 and use M 0.5 intervals) – Make a 3 column table of • Magnitude • total number of earthquakes greater than or equal to a specified magnitude • number/year • Plot this information on the graph provided (or use Excel) How might this information help to forecast future earthquakes? Questions to discuss with your partner • Do you see any patterns or trends in earthquake occurrence in the 2 regions? • What is the likelihood that an earthquake of magnitude 7.0 or greater (which can cause severe damage) will occur in the next year in the 2 regions? • How might this information be useful to society? • Is there a risk for forecasting earthquake likelihood using a data set that only goes back to 1973? Earthquakes, Magnitude >3.5, 1973-2007 Earthquakes, Magnitude >3.5, 1973-2007 Questions • What is the likelihood that an earthquake of magnitude 7.0 or greater will occur in the next year in the 2 regions? • How might this information be useful to society? • Is there a risk for forecasting earthquake likelihood using a data set that only goes back to 1973? What is the probability of an M6 event next year? Gutenberg-Richter Plot California Eastern US Expon. (California) Expon. (Eastern US) 1000.00 Number/Year 100.00 10.00 1.00 0.10 0.01 3 .5 4 4 .5 5 5 .5 6 Magnitude 6 .5 7 7 .5 8 8 .5 What is the probability of an M7 event next year? Gutenberg-Richter Plot California Eastern US Expon. (California) Expon. (Eastern US) 1000.00 Number/Year 100.00 10.00 1.00 0.10 0.01 3 .5 4 4 .5 5 5 .5 6 Magnitude 6 .5 7 7 .5 8 8 .5 Are the numbers of earthquakes in the smallest and largest ranges consistent with the trends in the other regions? Can you think of any reasons why the trend is “flat” for small and also large magnitudes? 1973-2007 10-3 10-4 10-5 N 10-6 10-7 10-8 10-9 Magnitude N = earthquakes per km2 per yr Ground shaking from a magnitude 6 earthquake in the east is approximately equivalent to that of a magnitude 7 earthquake in the west. http://pasadena.wr.usgs.gov/office/hough/east-vs-west.jpg 2002 National Seismic Hazard Map Although we can’t predict earthquakes (in the sense of predicting a specific time, location and magnitude)… Earthquake Hazard Analysis Global Seismic Hazard Map We can estimate the probability that a given amount of ground shaking will occur during a given period of time at some location. Japanese Folklore: Earthquakes caused by giant Namazu. Following the 1755 Lisbon earthquake on All Saint’s Day, the Spanish Inquisition burned people at the stake to atone for the city’s sins. Earthquake Prediction: Precursory Events Ex/ 1989 Loma Prieta Earthquake Also: Resistivity, water pressure and well levels, geyser activity, changes in seismicity Earthquake Prediction: Animal Behavior?? The exception: Feb 4, 1974: Haicheng, China * Almost no details are known of this. Another Approach: Forecasting Seismic “Gap” Hypothesis OLD Map of “Seismic Gap” Predictions Parkfield was in correct place, but very late. Northridge, Landers, Joshua Tree and Big Bear Earthquakes were not even on this map!!! “New York City Bear Gap” Hypothesis Parkfield, California, showed evidence of the recurrence of similar-sized (M 6.0) earthquakes In 1985 a 6.0 Parkfield earthquake was predicted with 95% confidence to occur by 1993. Mean = (1966-1857)/5 = 22 years Expected date = 1988 Didn’t occur until 2004 (16 years late!) Was it a success? Right size, right location, wrong date. Paleoseismology Extend earthquake history with geologic record Sieh et al., 1989 M >7 mean = 132 yr s = 105 yr Estimated probability in 30 yrs 7-51% However, even earthquake recurrence along plate boundaries is highly variable; probabilities hard to assess M>7: mean = 132 yr s = 105 yr Estimated probability of next earthquake in 30 yrs is 7-51% Random! Elastic Rebound (Seismic Gap) Theory? Sieh et al., 1989 NY City Bear Gap Hypothesis? Random seismicity simulation