Uncertainty in Earthquake Source Characterization for the L.A. Basin

DATE: September 18-19, 1997

LOCATION: USC Davidson Conference Center, Los Angeles, CA

CONVENORS: Bill Foxall, Norm Abrahamson, and Allin Cornell

An important source of uncertainty in seismic hazard estimates for southern California is uncertainty in the geometries (and in some cases the existence) of major faults that are potential sources of damaging earthquakes. This (epistemic) uncertainty stems from the fundamentally different models of tectonic deformation that have been proposed for parts of the region, and is particularly significant to estimation of hazard in the Los Angeles and Ventura Basins. Since the existing tectonic models are in large part mutually exclusive, it is not possible to combine parts of them into a "consensus" geological source model. Therefore, in order to capture the uncertainty in source geometry characterization a set of internally consistent source models that spans the alternative viable tectonic models is required. The models and their associated magnitude recurrence parameters can then be combined (for example, using an "event tree" method) in probabilistic seismic hazard analyses, thus enabling the epistemic uncertainty to be propagated through to uncertainty in hazard estimates.

The goals of the workshop are: (1) To develop a set of internally consistent alternative source models for the Los Angeles region that represents the consensus view of the SCEC community; and (2) through the exchange of current information and a directed debate of the evidence for and against each of the tectonic interpretations, to provide the basis for determining a set of relative weights for the source models and their component sources and parameter values. The workshop will follow a simple form of the procedures recommended by the Senior Seismic Hazards Analysis Committee ("Recommendations for Probabilistic Seismic Hazard Analysis; Guidance on Uncertainty and the use of Experts", NUREG/CR-6372, 1997; see also National Research Council review of this document, NRC Committee on Seismology, Washington, 1997). The meeting will include about twenty invited talks that will present the existing tectonic models and recent data and results that have a bearing on them, and directed discussion sessions in which the source models will be developed and queried, challenged and defended. A panel of knowledgeable evaluators will be asked to contribute to the debate and to weight the source models based on the evidence presented. The objective is not to conclude that one model is right and the others wrong, or to establish a single "consensus" model, but rather to allow all viable models to contribute to subsequent hazard predictions through a consensus set of weights reflecting the community's current uncertainty. Confirmed speakers to date are: John Shaw, Allin Cornell, Dan Ponti, Karl Mueller, Jim Dolan, Egill Hauksson, Ken Hudnut, and members of the LARSE team.

PRELIMINARY WORKSHOP AGENDA

Sept. 18
8:30	Welcome and introduction	B. Foxall
8:40	Uncertainty and expert opinion in probabilistic seismic hazard analysis	A. Cornell
9:05	Overview of alternative tectonic deformation models and earthquake source characterization for the Los Angeles Basin	B. Foxall
9:20	Geological constraints: Faulting and folding in the Los Angeles region	J. Dolan
9:50	Crustal deformation constraints in the Los Angeles Basin from continous GPS measurements since the Landers earthquake	Y. Bock
10:15	Break
10:25	Constraints on tectonic deformation and structure from seismicity and travel time tomography.	E. Hauksson
11:00	Constraints on seismic hazard models for the Los Angeles Basin from historical seismicity and moment rates	M. Petersen
11:20	Blind thrust faults in the Los Angeles Basin: Dealing with uncertainties in subsurface geological interpretation.	J. Shaw
12:00	Lunch
1:00	Tectonic style and fault slip rates in the eastern Ventura Basin, San Fernando Valley and northern Los Angeles Basin.	R. Yeats
1:40	Oblique thrust reactivation of listric faults, wide forelimbs, and propagating basin renewal-to-inversion, S. California	C. Sorlien
2:05	Kinematics and rates of faults south of the Transverse Ranges and an extrusion tectonic model for the Los Angeles Basin	T. Rockwell
3:00	Break
3:10	Deformation rate and style derived from tectonic geomorphology, downtown and eastern Los Angeles	M. Oskin
3:35	Recency of folding along the Compton-Los Alamitos trend: Implications for seismic hazard in the Los Angeles Basin.	K. Mueller
4:00	Constraints on deformation and blind thrust faulting in the northern Los Angeles Basin from Quaternary chronostratigraphy.	D. Ponti
4:20	Discussion
5:15	Adjourn

Sept. 19
8:00	Tectonic deformation modeling in the Los Angeles region: Comparison with geologic models.	(TBA)
8:30	Continuum mechanical models of fault-related folding	B. Hager
8:55	Evidence for subsurface structures under the Los Angeles Basin and San Gabriel mountains from seismic imaging	D. Okaya G. Fuis
9:15	Discussion
9:45	Break
10:00	Three-dimensional seismo-tectonic imaging: An example from the California southern Transverse Ranges.	P. Geiser
10:25	"Strawmen" alternative earthquake source characterizations.	B. Foxall
10:55	Sensitivity of seismic hazard in the Los Angeles Basin to alternative earthquake source characterizations.	N. Abrahamson
11:20	Interactive session to modify/construct alternative source models.	led by B. Foxall, N. Abrahamson, and A. Cornell
12:30	Lunch
1:30	Presentations and feedback on preliminary weighting of alternative source characteristics	Evaluator panel
2:30	Adjourn

Registration Form
If you are planning to attend, please enter the information in the boxes provided, then click on "Submit" to e-mail your registration.

First Name
Last Name
Organization
Street Address
City
State
Zip Code
Phone Number
Fax Number
E-mail