Prediction of Natural Disasters Art Lerner-Lam Associate Director Doherty Senior Research Scientist Adjunct Professor Lamont-Doherty Earth Observatory of Columbia University
Prediction of Natural Disasters • What is a “Natural Hazard”/“Natural Disaster”? • What is the difference between “hazard” and “risk”? • Are natural hazards predictable? • What constitutes a “prediction”? • What role does science play in response?
What is a “Natural Hazard/Disaster”? • A natural hazard is a natural process that has the potential for significant human impacts. • A natural disaster is the occurrence of a natural event with significant human and social impacts.
Events earthquakes, volcanoes, landslides hurricanes, typhoons, Nor’easters, hailstorms, blizzards, icestorms droughts, heatwaves forest fires bolide impacts Trends global warming sea-level rise ground-water loss ozone loss disruption of cycles (carbon, nitrogen, hydrological) anthropogenic forcing Types of Natural Hazards
Man is a geologic force • Anthropogenic forcing is a significant factor in climate change. • Land-use practices put humans in danger. • Human society has an impact on the Earth that is significant in scope and scale.
What is “scale”? • Processes have characteristic spatial and temporal scales • Events/trends at one scale may be manifestations of events/trends at another scale Length scale Characteristic time scale t
Examples of Scale Simple, linear processes can maintain scale superposition. That is, the total process is just the sum of sub-processes each with its own scale. Complex and non-linear processes possess complex scale interdependencies. The dynamics at one scale can influence the dynamics at another scale. Scale interdependencies make prediction especially hard, since the driving forces may not be known.
Process interactions • Human impacts must be aggregated • One process can amplify impacts of another process
“Hazard” is a process which has potential human impacts. “Risk” is the “product” of hazard and accumulated human assets. “Concentration of wealth” matters. What is the difference between “Hazard” and “Risk”? Source: USGS
Probabilistic earthquake hazard expressed as level of ground acceleration that has a 10% chance of being exceeded in the next 50 years.
Population is just one of the possible proxies for quantifying human impact.
Risk is relative • Developed and underdeveloped societies have different asset exposures. • System effects can compound the valuation of risk. • The study of risk is a social science.
Are Natural Disasters Predictable? • definition of prediction • scientific approach to prediction • Assume plate tectonic kinematic conditions apply to earthquake loading cycle. • Earthquakes occur on known faults. • In intraplate regions, earthquakes occur where they have occurred before.
What is a “Prediction”? • Predict an “event”. • specify place, time, and size, in advance • specify impacts, in advance • Predict event potential • specify zones of space and time within which events might occur • specify impact scenarios
Model-based or Empirical? • use previous event patterns to predict new occurrences. • or, develop and test a model • characteristic earthquake model is simple but requires empirical calibration • newer models are being developed which include non-linear effects
Empirical studies require: • long “time series” • careful identification and selection of associate conditions • knowledge of the probability distribution
Modeling studies require: • physical (or chemical) understanding of process • representational theorems and constitutive relations • realistic parameterizations • ability to model complexity, chaos, and non-linearity if needed.
Plate tectonic theory is more space-predictable than time-predictable on human time scales.
Characteristic Earthquake Model • apply plate tectonic boundary conditions to earthquake cycle time scales • assume plate tectonic loading applies to intraplate earthquakes • develop characteristic recurrence times and recurrence-size relationships log (number) log (magnitude)
Implications of Characteristic Earthquake Model characteristic time slip predictable characteristic size time predictable time
Characteristic earthquake assumption permits computation of Global Hazard MapSource: USGS GSHAP Project
WUS Fault Map Source: CDMG