WGCEP Workshop

What Represents Best Available Science

in terms ofTime-Dependent Earthquake

Probabilities?

Introduction by Ned Field

Best Available Science?

Poisson Model (long-term rates)

Quasi-Periodic Recurrence Models• BPT Renewal

• Time or Slip predictable

Static-Stress Interaction Models• Clock change

• BPT-step

• Rate & State

• Clock change w/ Rate & State

• Hardebeck (2004) approach

Empirical Rate Change Models

Clustering Models

• Foreshock/Afershock statistics (e.g., STEP; ETAS)

Summary (in brief) of Previous:

“Working Groups on California Earthquake Probabilities”

(WGCEP, 1988, 1990, 1995, 2002)

They generally segmented faults and applied elastic-rebound-theory-motivated (quasi-periodic) renewal models to define time-dependent earthquake probabilities ...

Reid’s (1910) Elastic Rebound Hypothesis:

EQ

Time

Stress

Loadi

ng

Stress

Loadi

ng

Stress

Loadi

ng

EQ EQ

Stress

Loadi

ng

EQ

morenoisysystem

PerfectlyPeriodic

LognormalorBPT

distribution

Reid’s (1910) Elastic Rebound Hypothesis:

They divided the San Andreas, San Jacinto, Hayward, and Imperial Faults into segments and assumed each ruptures only in a single-magnitude (“characteristic”) earthquake.

WGCEP 1988

WGCEP 1988

COVI = 0.2

Mean Recurrence Interval from:

1) Ave of those observed previously.

2) Slip in last event divided by slip rate.

3) Ave slip divided by slip rate.

WGCEP 1990

Updated WGCEP (1988) for San Francisco Bay Area in light of the 1989 Loma Prieta earthquake (and some new data).e.g., applied a clock change to account for influence of Loma Prieta on Peninsula segment (seg #3).

€

ΔT =StressChange

StressRate≈11yrs

Focused on southern Cal. (SCEC’s Phase II report).

2) Allowed neighboring segments to sometimes rupture together as “cascade” events3) Included lesser faults and background seismicity (to account for unknown faults)

Innovations:

WGCEP 1995

1) Updated WGCEP (1988) segment probabilities (COVI = 0.5 +/- 0.2)

WGCEP 1995

Problem: predicted twice as many mag 6-7 events as have been observed historically, which led to a lively debate on this apparent earthquake “deficit”:Need to allow “huge” events

(Mag≥8)potentially anywhere (Jackson,

1996)But such events would leave obvious scars(Schwartz, 1996; Hough, 1996)

Problem results from several factors;solution exists (e.g., Stirling and Wesnousky (1997); Stein & Hanks (1998); and Field et al., (1999))

WGCEP 1995

Problem: predicted twice as many mag 6-7 events as have been observed historically, which led to a lively debate on this apparent earthquake “deficit”:Need to allow “huge” events

(Mag≥8)potentially anywhere (Jackson,

1996)But such events would leave obvious scars(Schwartz, 1996; Hough, 1996)

Problem results from several factors;solution exists (e.g., Stirling and Wesnousky (1997); Stein & Hanks (1998); and Field et al., (1999))

Note:

these two were part of the working group …

implying a lack of “consensus” …

RELM

Focused on Bay Area

2) “Consensus process” rather than consensus model

3) Extensive treatment of epistemic uncertainties (logic-tree branches)

Other Innovations:

WGCEP 2002

1) Updated WGCEP (1990) segment probabilities based on a more elaborate earthquake rate model; allowed cascades

Current

Working Group on California Earthquake Probabilities

(WGCEP)

Development of a

Uniform California Earthquake Rupture Forecast

(UCERF)

22% of our funding comes from the

California Earthquake Authority (CEA)

Northridge caused 93% of insurers to halt or significantly reduce coverage.

CEA was created (via state legislation) to resolve the crisis.

CEA is a privately financed, publicly managed (and tax exempt) organization that offers basic earthquake insurance for California homeowners and renters.

It’s governed by: CA Governor, Treasurer, Insurance Commissioner, Speaker of the Assembly, and Chairperson of the Senate Rules Committee.

CEA policies are sold only through participating insurance companies (two-thirds of California homeowners policies).

Policies carry a 15% deductible.

Today the CEA has $7.2 billion to pay claims.

CEA is required by law to use “best-available science”.

California Earthquake Authority (CEA):

Best Available Science?

California Insurance Code section 10089.40 (a)

"Rates shall be based on the best available scientific information for assessing the risk of earthquake frequency, severity and loss.”

“Scientific information from geologists, seismologists, or similar experts shall not be conclusive to support the establishment of different rates … unless that information, as analyzed by experts such as the United StatesGeological Survey, the California Division of Mines and Geology, and experts in the scientific or academic community, clearly shows a higher risk of earthquake frequency, severity, or loss between those most populous rating territories to support those differences.”

“Seismic Event”

“Seismic Event” means one or more earthquakes that occur within a 360-hour period. The seismic event commences upon the initial earthquake, and all earthquakes or aftershocks that occur within the 360 hours immediately following the initial earthquake are considered for purposes of this policy to be part of the same seismic event.

from page 6 of CEA’s “Basic Earthquake Policy--Homeowners” doc

Coordinated with the next National Seismic Hazard Mapping Program (NSHMP) time-independent model

This will be used by CEA to set earthquake insurance rates (they want 5-year forecasts, maybe 1-year in future)

WGCEP Goals:

1988 1990 1995

2002

UCERF

To provide the California Earthquake Authority (CEA) with a statewide, time-dependent ERF that uses “best available science” and is endorsed by the USGS, CGS, and SCEC, and is evaluated by a Scientific Review Panel (SRP), CEPEC, and NEPEC

NSF

CEA

USGS

CGS

SCEC

MOC

State of CA

USGS Menlo Park

USGS Golden

Sources of WGCEP funding

Geoscience organizations

Management oversightcommittee

WGCEPExCom

Subcom.A

Subcom.B

Subcom.C

…

…

Working group leadership

Task-oriented subcommittees

Working Group on California Earthquake

Probabilities

WGCEP Organization

& Funding Sources

SCEC will provide CEA with a single-point interface to the project.

SRP

Scientific reviewpanel

Thomas H. Jordan (SCEC, Chair) Rufus Catchings (USGS, Menlo Park ) Jill McCarthy (USGS, Golden ) Michael Reichle (CGS)

Ned Field (USGS, Chair) Thomas Parsons (USGS, Menlo Park) Chris Wills (CGS) Ray Weldon (U of O) Mark Petersen (USGS, Golden) Ross Stein (USGS, Menlo Park)

Bill Ellsworth (chair)Art FrankelDavid JacksonSteve WesnouskyLloyd CluffAllin CornellMike BlanpiedDavid Schwartz

Plus many others

Delivery Schedule

February 8, 2006 (to CEA)

UCERF 1.0 &

S. SAF Assessment to CEA

Aug 31, 2006 (to CEA)

Fault Section Database 2.0

Earthquake Rate Model 2.0 (preliminary for NSHMP)

April 1, 2007 (to NSHMP)

Revised Earthquake Rate Model 2.x(for use in 2007 NSHMP revision)

September 30, 2007 (to CEA)

UCERF 2 (reviewed by SRP, NEPEC, and CEPEC)

1) Everything takes longer than you

expect

• Some planned on innovations won’t

pan out

• Focus on what’s important

2) There will be problems with the final

model

• The best time to solve these

problems is right away (while fresh

in the mind)

• Burnout makes this problematic

Important Lessons from Previous WGCEPs:

Thus: • Plan for both the near and long term

(e.g., build a living, adaptive, extensible infrastructure)

Deploy as extensible, adaptive (living) model

i.e., modifications can be made as warranted by scientific developments, the collection of new data, or following the occurrence of significant earthquakes. The model can be “living” to the extent that update & evaluation process can occur in short order.

How do we plan to achieve this?

BlackBox

Deformation

Model(s)

Earthquake Prob Model(s)

Earthquake Rate Model(s)

BlackBox

BlackBox

UCERF Model Components(generalization of WGCEP-2002)

FaultModel(s)

The computer code

The models &/orapplications

Object Oriented (Modular) Framework - building on OpenSHA

BlackBox

Deformation

Model(s)

Earthquake Prob Model(s)

Earthquake Rate Model(s)

BlackBox

BlackBox

UCERF Model Components(generalization of WGCEP-2002)

FaultModel(s)

Fault-slip rates (at least)

Long-term rate of all possible events (on and off modeled faults)

Time-dependent probabilities

BlackBox

Deformation

Model(s)

Earthquake Prob Model(s)

Earthquake Rate Model(s)

BlackBox

BlackBox

FaultModel(s)

Fault Section Database

Paleo Sites

Database

GPS Database

Historical Qk

Catalog

Instrumental Qk Catalog

UCERF Model Components

BlackBox

Deformation

Model(s)

Earthquake Prob Model(s)

Earthquake Rate Model(s)

BlackBox

BlackBox

UCERF Model ComponentsFaultModel(s)

Object Oriented(Modular) Framework

Makes logic trees very easy to handle …

OpenSHA Hazard Curve Calculator

WGCEP-2002 Hazard Curves (Field et al. 2005, SRL)

Distributed Object Technologies (Maechling et al., 2005, SRL)

WGCEP-2002 (10,000 branches)

Now w/ NGAs & ERM 2.2 also

Issue with Logic Trees

1) They take time and resources to implement and document

2) Must be careful about correlations (Page and Carlson, 2006, BSSA)

3) Is anyone using them?

4) How do we know which are important or worth pursuing (especially in terms of loss)?

Demo Loss Calculator?

Logic Trees

What we need is not all possible branches, but the minimum number of branches that span the range of viability and importance

Best Available Science?

Poisson Model (long-term rates)

Quasi-Periodic Recurrence Models• BPT Renewal

• Time or Slip predictable

Static-Stress Interaction Models• Clock change

• BPT-step

• Rate & State

• Clock change w/ Rate & State

• Hardebeck (2004) approach

Empirical Rate-Change Models

Clustering Models

• Foreshock/Afershock statistics (e.g., STEP; ETAS)