Earthquake Hazard, Risk and Protection Policy

Abstract:

Policy makers need to know how large future earthquake disasters are likely to be and what part of the population is in harm’s way. The tools available for seismic hazard assessment are: 1) Geological mapping and trenching of active faults, 2) geodetic deformation measurements of the crust, 3) historical records of earthquakes. The data necessary for risk assessment are: a) Population of all settlements. b) Resistance of the built environment in different size settlements to ground motions. c) Algorithms to calculate building damage, fatalities and injured. d) Ground motion prediction equations. We select regions where large earthquakes at return times that are not more than a few hundred years are known to occur, applying deterministic models of fault segments likely to break in one earthquake. We validate our computer program requiring it to match the intensity field or accelerations and fatalities reported for historic earthquakes. As measure of the size of the expected disaster in our tool QLARM, we use the total estimated numbers of fatalities and people affected. The numbers of injured people is poorly defined or not given for historic earthquakes, thus estimates are uncertain. We define the number of people affected and strongly affected as those living in the areas with intensities VI and VII, and VIII+, respectively. In worldwide estimates of the ratio of rural/urban fatalities we have found that in great earthquakes 90% are rural fatalities. However, in densely populated countries with mostly large (not great) earthquakes that ratio can be as low as 20%. Thus the parameters on which policy makers need to make decisions concerning earthquake protection are expected numbers of fatalities and injured, affected people in the two mentioned intensity classes, plus the percentage of urban casualties. The damage likely sustained by critical facilities, such as hospitals and schools, should be calculated and included in the list of important inputs for policy makers, and especially first responders, but this cannot be done at present. For most countries, the locations and sizes of hospitals and schools are currently not known. A major effort should be launched to make available parameters of critical facilities.