11. Probabilistic Seismic Risk Analysis for Buildings Subjected to Sequences of Large Earthquakes

Earthquake aftershocks and foreshocks are not included in typical probabilistic seismic hazard analyses (PSHAs), including those conducted to produce the USGS National Seismic Hazard Maps (NSHMs) ( http://earthquake.usgs.gov/research/hazmaps/).  In fact, aftershocks and foreshocks are deliberately removed from the catalogs of historical earthquakes used in these PSHAs, in order to be consistent with the typical assumption of independent earthquakes in time (i.e., time-independence).  Since probabilistic seismic risk (or loss) analyses, abbreviated here as PSRAs, extend PSHAs in order to quantify the potential for future earthquake damage to buildings (or other structures, e.g., bridges), they do not typically include the effects of foreshocks and aftershocks either.  It is generally assumed that there is negligible damage associated with aftershocks and foreshocks.  Depending on the location and magnitude of an aftershock or foreshock, however, the ground motions it produces at the location of a building can be larger and more damaging than those resulting from the mainshock.  This possibility is reflected in the time-dependent “24-Hour Aftershock Forecast Maps” that the USGS now produces for California (http://pasadena.wr.usgs.gov/step/).

Besides foreshock-mainshock-aftershock sequences, buildings might also be subjected to clusters of large earthquakes over a relatively short time period, such as the sequence of three large earthquakes (magnitude 7 or greater) observed over 1811-1812 in the New Madrid Seismic Zone.  Since geologic evidence in that area suggests that earlier large earthquakes also occurred in sequences of three, a clustered-earthquakes model has been incorporated into the PSHAs conducted for the recently-completed 2008 update of the USGS NSHMs.  For PSRAs based on these PSHAs, however, it is generally assumed that either a building is damaged by only one of the clustered earthquakes, or there is adequate time for structural repairs between earthquakes; clearly this is not always the case.

The PSHA models of aftershocks and clustered earthquakes described above provide starting points for PSRAs that account for sequences of damaging earthquakes too closely-spaced in time to allow for structural repairs.  Like in typical PSRAs, the ground motion hazard information can be coupled with structural fragility or vulnerability models that relate ground motion amplitudes to probabilities of failure (e.g., collapse) or probability distributions of losses (e.g., costs of repair), respectively.  The primary difference is that the fragility and vulnerability models must account for the state of damage after the preceding earthquake (e.g., the mainshock or the first earthquake in a cluster), which cannot be known without uncertainty.  Fortunately, this uncertainty in the state of damage can be reduced via (1) simulations of the structural response to the preceding earthquake, (2) partial visual inspections of the building after the earthquake, and/or (3) data from instruments that record the structural response and/or nearby ground motions.  The fragility and vulnerability of the damaged building can be modeled via nonlinear dynamic structural analyses (NDA) under seismograms corresponding to each in a range of ground motion amplitudes, like they are for undamaged buildings in typical PSRAs.  The primary information resulting from the PSRAs for earthquake sequences is still the risk of structural failure or excessive losses, either before (as is the case for typical PSRA) or after a damaging earthquake has occurred.  Potential uses of such information include (1) objectively and perhaps even remotely decide on a green, yellow, or red occupancy tag for a building after a damaging earthquake, based on the risk of collapse of the damaged building in an aftershock (or subsequent earthquake) relative to the risk before the damaging earthquake, (2) assess the risk for a structural design or for existing building that might be exposed to a cluster of damaging earthquakes, and (3) quantify the potential cumulative losses sustained by a building during the 72-hour period after a damaging earthquake that is typically covered by a single insurance claim.

We seek a Mendenhall Fellow with seismologic or civil engineering expertise who would research methodologies for and/or components of PSRAs for sequences of damaging earthquakes.  Examples of such research include (1) providing feedback on available PSHA models for aftershocks or clustered earthquakes and/or their outputs in light of their use for the PSRAs, (2) advancing existing procedures for deriving fragility or vulnerability models for a building in an uncertain state of damage caused by a preceding earthquake, and (3) developing new ways of combining the aforementioned hazard and vulnerability models.  More specific examples of (2) include defining a new procedure for selecting appropriate seismograms that are representative of aftershocks or clustered earthquakes for the NDAs of the building, and using structural response and ground motion instrumentation data to constrain the uncertainty in the state of damage of a building, e.g., via Bayesian updating. Such advancements could be demonstrated for archetypical buildings. 

References

Bazzurro, P., Cornell, C.A., Menun, C., Motahari, M., and Luco, N., 2006, Advanced seismic assessment guidelines: Pacific Earthquake Engineering Research Center (PEER) Report 2006/05 (http://peer.berkeley.edu/publications/peer_reports/reports_2006/web_PEER605_BAZZURRO_etal.pdf).

Celebi, M., Page, R.A., and Safak, E., 2003, Monitoring earthquake shaking in buildings to reduce loss of life and property: U.S. Geological Survey Fact Sheet 068-03 (http://pubs.usgs.gov/fs/2003/fs068-03/).

Gerstenberger, M., Wiemer, S., and Jones, L., 2004, Real-time forecasts of tomorrow’s earthquakes in California: A new mapping tool: U.S. Geological Survey Open-File Report 2004-1390 (http://pubs.usgs.gov/of/2004/1390/).

Luco, N., Bazzurro, P., and Cornell, C.A., 2004, Dynamic versus static computation of the residual capacity of a mainshock-damaged building to withstand aftershocks, in Proceedings of the Thirteenth World Conference on Earthquake Engineering, Paper No. 2405, p. 113-127 of http://peer.berkeley.edu/lifelines/lifelines_pre_2006/final_reports/1G00-FR.pdf.

Petersen, M.D., Frankel, A.D., Harmsen, S.C., Mueller, C.S., Haller, K.M., Wheeler, R.L., Wesson, R.L., Zeng, Y., Boyd, O.S., Perkins, D.M., Luco, N., Field, E.H., Wills, C.J., and Rukstales, K.S., 2008, Documentation for the 2008 update of the United States National Seismic Hazard Maps: U.S. Geological Survey Open-File Report 2008-1128 (http://pubs.usgs.gov/ of/2008/1128/).

Wald, D.J., Worden, B.C., Quitoriano, V., and Pankow, K.L., 2003, ShakeMap – A tool for earthquake response: U.S. Geological Survey Fact Sheet 087-03 (http://pubs.usgs.gov/fs/fs-087-03/).

Yeo, G.L., and Cornell, C.A., 2005, Stochastic characterization and decision bases under time-dependent aftershock risk in performance-based earthquake engineering: Pacific Earthquake Engineering Research Center (PEER) Report 2005/13 (http://peer.berkeley.edu/publications/peer_reports/reports_2005/PEER513_YEO_cornell.pdf).

Proposed Duty Station: Golden, CO

Areas of Ph.D.: Seismology, civil engineering

Qualifications: Applicants must meet one of the following qualifications: Research Geologist, Research Geophysicist, Research Engineer

(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)

Research Advisor(s): Nicolas Luco, (303) 273-8683, nluco@usgs.gov; Mark Petersen, (303) 273-8546, mpetersen@usgs.gov; David Wald, (303) 273-8441, wald@usgs.gov; Mehmet Celebi, (650) 329-5623, celebi@usgs.gov; Paolo Bazzurro (AIR Worldwide Corporation), (415) 912-3111, pbazzurro@air-worldwide.com; Matt Gerstenberger (Institute of Geological and Nuclear Sciences, New Zealand), 64-(4) 570-4554, m.gerstenberger@gns.cri.nz; Erdem Karaca (Swiss Re), (914) 828-8405, Erdem_Karaca@swissre.com

Human Resources Office contact: Vanessa Chambless, (303) 236-9584, vchambless@usgs.gov

Summary of Opportunities