About Earthquake Hazards By Sergio Espinosa

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About Earthquake Hazards By Sergio Espinosa

  1. 1. Earthquake Hazards Sergio Espinosa, Ph.D. Geophysics
  2. 2. Natural disasters can always be described in a time axis: time before time after the natural event the natural event happens has happened time time when now the natural event is happening Sergio Espinosa, Ph.D. Geophysics
  3. 3. BEFORE the natural event time during now the natural event Sergio Espinosa, Ph.D. Geophysics
  4. 4. BEFORE the natural event: Increase preparedness and awareness. Conduct risk assessments Risk = Hazard * Vulnerability Hazard - (1) Traffic level in a street Natural processes, normally out of our control - (2) Rain Vulnerability - (1) Physical Fitness to cross the street Conditions we can manage - (2) Umbrella size and quality Sergio Espinosa, Ph.D. Geophysics
  5. 5. Hazards Conditions and associated processes, normally out of our control • Natural hazards - extra-terrestrial (e.g. meteoritic impact) - meteorological (e.g. hurricane, floodings) - geological (e.g. volcano, earthquake) • Also technical and man-made hazards Sergio Espinosa, Ph.D. Geophysics
  6. 6. Vulnerabilities Conditions we normally can manage • Population density and exposure • Preparedness, public health • Abilities and capacities to respond and mitigate • Governance and free will • Knowledge, education • Buildings and structures, technical vulnerabilities • etc. Sergio Espinosa, Ph.D. Geophysics
  7. 7. time DURING now the natural event Sergio Espinosa, Ph.D. Geophysics
  8. 8. DURING the natural event: A natural event might take from seconds or minutes (the fall of a meteorite, an earthquake, a landslide), to hours or days (main seismic event and its after- shocks, a volcanic eruption, a hurricane, a bush fire, a winter storm, floods), to months or years (draught) . We do not know when and where it will happen, but we know that IT WILL HAPPEN some time and some where. The question is how severe and how probable? in a specific site and in a time frame? Individual and collective response, assistance, etc. Sergio Espinosa, Ph.D. Geophysics
  9. 9. AFTER the natural event time during now the natural event Sergio Espinosa, Ph.D. Geophysics
  10. 10. AFTER the natural event: Immediate disaster relief, recovery, reconstruction… Remembering. Since this time AFTER the last natural event is also a time BEFORE the next one, it is a time to learn, to improve preparedness, to be more aware, … … and to improve risk assessments. Sergio Espinosa, Ph.D. Geophysics
  11. 11. The time after a first natural event… …becomes the time before the next one time before time after the first natural event the first natural event time before next natural event time first natural event next natural event now Sergio Espinosa, Ph.D. Geophysics
  12. 12. Time before the next natural event Natural hazard assessments have different time scales: e.g. Weather forecasting. Monitoring of hurricanes, volcanoes, deformations, induced micro-seismicity (rock bursts) etc. Short-term ‘Prediction’ and Long-term Forecasting (e.g. 3d) Assessments (e.g. 100 a) e.g. Earthquake Hazards time Middle-term Prognosis (e.g. 1a) e.g. El Nino next natural event now A probability level (e.g. “30% probability of rain”) and an “uncertainty fan” is always associated to all time scales !!! Sergio Espinosa, Ph.D. Geophysics
  13. 13. http://www.nhc.noaa.gov/archive/2007/graphics/al04/loop_5W.shtml Sergio Espinosa, Ph.D. Sergio Espinosa, Ph.D. Geophysics Geophysics
  14. 14. not probable most Explanation of probable probable ‘Uncertainty Fan’ using a 36 hr Hurricane Trajectory probable as an example 24 hr not probable 12 hr 6 hr 1 hr now Sergio Espinosa, Ph.D. Geophysics
  15. 15. Long-term Earthquake Hazard Assessments Definition of its quantification: Probability (P) that in a specific region (r) and in a specific time frame (t), a seismic event will occur that will exceed a certain energy value (E). P = f (r,t,E) or E = f (r,t,P) if time (t) and probability (P) are kept constants then E = f (r) maps Sergio Espinosa, Ph.D. Geophysics
  16. 16. Long-term Earthquake Hazard Assessments The energy value (E) can be expressed as the energy released in the seismic source (magnitude Mw) or as the energy received in a specific site, as the soil vibration in terms of soil displacement (d), velocity (v), or acceleration (a) in the time range (seismograms) and/or in the frequency range (spectra). However, soil vibration can only and always be quantified with instruments. However, if instrumental information is not available, then another valid site parameter can be used: the Observed Intensities. Sergio Espinosa, Ph.D. Geophysics
  17. 17. Relation between Seismic Source and Hazard Site epicentral and/or maximal Site X where hazard level intensity will be determined IEPI = IMAX IX Earth Surface Seismic Wave Propagation Seismic Source (quantified with V- or Q- Magnitude Mw tomography) (quantified with focal mechanism techniques) Sergio Espinosa, Ph.D. Geophysics
  18. 18. Spatial-temporal quantification and energy balance of the seismic source Earth Surface Seismic Source Sergio Espinosa, Ph.D. Geophysics
  19. 19. Spatial-temporal quantification and energy balance of the seismic source Achieved with instrumental observations and paleo-seismological techniques Gutenberg and Richter relation N is the number of seismic events in Log (N) a specific time period with magnitud Mw Log (N) = a – b * Mw a and b are linearity coefficients. However, it doesn’t behave linearly for large events. Mw b-value depends on the tectonic regime and on the rheology of the seismic source Sergio Espinosa, Ph.D. Geophysics
  20. 20. Quantification of the seismic wave propagation Earth Surface Seismic Wave Propagation and Seismic Source Energy Attenuation Sergio Espinosa, Ph.D. Geophysics
  21. 21. Quantification of the seismic wave propagation Seismic (elastic) energy is attenuated during its path from the seismic source to the site where the hazard level will be estimated. Attenuation depends e.g. on the regional thermal regime. Received energy (E) in the site is quantified as seismogram amplitudes and depends firstly on the magnitude (Mw) of the seismic source, on the distance (D) from source to site, and on the geological conditions (G) between source and site. E = f (Mw,D,G) M: the stronger the earthquake, the more energy is received; D: the larger the distance to the source, the more energy is attenuated; G: magmatic arcs attenuate more energy. Sergio Espinosa, Ph.D. Geophysics
  22. 22. Dynamical quantification of site Site where hazard level will be determined Earth Surface Seismic Wave Propagation Seismic Source Sergio Espinosa, Ph.D. Geophysics
  23. 23. Dynamical quantification of site The arriving wave interacts with local site conditions. Amplification: Some soils amplify the amplitudes in certain frequency range. Liquefaction: Other soils liquefy depending on density, porosity, and water content. Landslides might also be triggered in other sites depending on slope and local geomechanical conditions. NB: These site effects are similar to “local anomalies” in geophysical exploration. Sergio Espinosa, Ph.D. Geophysics
  24. 24. Regional ‘Anomalies’ Acapulco, Mexico Sergio Espinosa, Ph.D. Geophysics
  25. 25. Local ‘Anomalies’ Acapulco, Mexico After Mendoza et.al. (2008) Sergio Espinosa, Ph.D. Geophysics
  26. 26. Long-term Earthquake Hazard Assessments Observation Calculation / Extrapolation in the past into the future (Exposure Time) time Frequency of Magnitudes now Probability of Ocurrence (Return Period) (Return Period) Sergio Espinosa, Ph.D. Geophysics
  27. 27. Long-term Earthquake Hazard Assessments Observation Time (OT) Exposure Time (ET) Certainty Long Short time Observed Frequency of Magnitudes Calculated Probability of Occurrence now Short Long Uncertainty Sergio Espinosa, Ph.D. Geophysics
  28. 28. Explanation of Uncertainty using the Uncertainty Hurricane Trajectory Analogy ET is large OT/ ET is small Certainty ET is small OT/ ET is large Sergio Espinosa, Ph.D. Geophysics
  29. 29. Observation Time Instrumental records 100 a Minimal detectable magnitude of seismic source depends on stations and arrays Historical records 1,000 a Reported intensity of site depends on population density and cultural development Neo-tectonic and paleo-seismological records 10,000 a Only strong events can be determined. However, weaker events represent a high risk too (e.g. Managua earthquake in December 1972; “weak” earthquake with 5.1 magnitude; 30,000 deaths and injured). Geological evidence needs to outcrop. Sergio Espinosa, Ph.D. Geophysics
  30. 30. Exposure Time This is an input parameter in the calculation process and is chosen depending on the observation time (completeness of information), so that results are ‘certain’, similar as in the hurricane trajectory analogy. For the insurance industry, the exposure time depends on the economic life of an asset. For government officials in urban planning, the exposure time might be longer. Sergio Espinosa, Ph.D. Geophysics
  31. 31. Results of a Macro-seismic Hazard Assessment for Nicaragua Sergio Espinosa, Ph.D. Geophysics
  32. 32. Used Data Seismic catalog compiled by Norsar (Norway) in coordination with seismological agencies of Central America. Catalog had information about location (lat, lon, depth), time (yy, mm, dd, hh, ss), released energy in the seismic source as magnitudes (mb, Ms, Ml), and received energy in the sites as epicentral and maximal intensities observed (Iepi and Imax). Unfortunately, no strong-motion (soil acceleration) records were available. So intensities needed to be used. Sergio Espinosa, Ph.D. Geophysics
  33. 33. Methodology Quality Control A QC-procedure needed first to be carried out (time completeness of information). Frequency of Magnitudes Seismogenic regions needed to be determined and each region needed to be studied separately so that the b-value of each region could be determined. Sergio Espinosa, Ph.D. Geophysics
  34. 34. Methodology Attenuation Relation By finding the attenuation parameters for the whole region, magnitudes could be calculated into hypothetical intensities. Statistical Model (Poisson) The probability was then calculated that a set of intensities is going to be exceeded in the region (map) for different exposure times. Sergio Espinosa, Ph.D. Geophysics
  35. 35. Regional ‘Anomalies’ Nicaragua Sergio Espinosa, Ph.D. Geophysics
  36. 36. Local ‘Anomalies’ in Nicaragua Macro-Seismic Hazard Map After Espinosa (1996) Sergio Espinosa, Ph.D. Geophysics
  37. 37. Local ‘Anomalies’ in Nicaragua Macro-Seismic Hazard Map After Espinosa (1996) Sergio Espinosa, Ph.D. Geophysics
  38. 38. Can we predict the time, location and size … … of these rain drops? Sergio Espinosa, Ph.D. Geophysics
  39. 39. Well,… the answer is “No” Then, let’s get prepared… … and by decreasing our vulnerability with better buildings and preparedness. By studying local site conditions, by assessing and quantifying its corresponding hazard level, by making the right decisions in urban planning … Sergio Espinosa, Ph.D. Geophysics
  40. 40. Thanks !!! Sergio Espinosa, Ph.D. Geophysics

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