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Organization Title

 HAZUS Loss Estimation for California Scenario Earthquakes

Rui Chen, David Branum, and Chris J. Wills
California Geological Survey
June 2009

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Summary

Using HAZUS, loss estimation software developed by the Federal Emergency Management Agency (FEMA), we estimated economic losses, social impact, and structural damage for fifty-six scenario earthquakes developed by the United States Geological Survey (USGS) (referred to as USGS scenarios).  These scenarios were developed using ground motion prediction equations (GMPEs) of Boore et al. 1997 for peak ground acceleration (PGA), spectral acceleration at 0.3 second (SA03), and spectral acceleration at 1.0 second (SA10), and of Joyner and Boore 1988 for peak ground velocity (PGV).  Source parameters, including magnitude and fault geometry, were based on the 2002 statewide probabilistic seismic hazard assessments for California.  Significant research developments have occurred in the past few years in both ground motion prediction and rupture source characterization.  To estimate how these latest developments affect HAZUS loss estimates, we developed and analyzed ten additional scenarios.  These scenarios were developed based on source parameters and probability results of the Uniform California Earthquake Rupture Forecast Version 2 (UCERF 2) completed in 2008 by the Working Group on California Earthquake Probabilities and are referred to as UCERF 2-based scenarios.  Three of the five Next Generation Attenuation (NGA) models were used to calculate PGA, PGV, SA03, and SA10 for the UCERF 2-based scenarios, namely models of Boore and Atkinson 2008, Campbell and Bozorgnia 2008, and Chiou and Youngs 2008.  These three NGA models were used in the 2008 Update of the National Seismic Hazard Maps by USGS.  The NGA models are founded on a significantly improved common database of ground motion recordings and to a large extent they have replaced earlier GMPEs for shallow crustal earthquakes in western United States.  These NGA models resulted in notable changes in predicted ground motions, particularly for long periods (see figure 1, for example).  One can expect that NGA models could lead to substantial differences in estimated losses and related effects than those derived from earlier GMPEs.  Our analyses show that the estimated losses for the UCERF 2-based scenarios are 28% – 63% lower than those for the comparable USGS scenarios.  Additional work is need to determine how the NGA models for earthquake shaking should be used in the HAZUS models for earthquake loss estimation.

 

Figure 1. Comparison of ground motions for a repeat of the 1906 M 7.9 San Francisco earthquake on the Northern San Andreas Fault (co-seismic rupture of all four segments).

Based on the analyses of the USGS scenarios in Northern California, the three most damaging scenario earthquakes involve co-seismic rupture of different combinations of three or more Northern San Andreas Fault segments, resulting in an estimated economic loss ranging from nearly $70 billion to over $80 billion (table 1).  The most damaging scenario earthquake is a repeat of the 1906 San Francisco M7.9 earthquake.  It would rupture all four segments of the Northern San Andreas Fault.  Estimates made using HAZUS suggest that this earthquake would cause nearly $84 billion of economic loss, mostly building related.  The scenario earthquake is estimated to kill 1000 to 4000 people, displace 64 thousand households, and generate 23 million tons of debris.  HAZUS calculations show at least moderate damage on nearly 700 locations of highway bridges, 7 locations of airports, 6 schools, and over 343 thousand buildings.  Other earthquakes with over $30 billion estimated losses in Northern California include: an M7.26 earthquake rupturing the entire Hayward-Rodgers Creek Fault causing $39 billion in losses and an M7.42 earthquake rupturing the Santa Cruz Mountain and Peninsula segments of the Northern San Andreas fault causing $36 billion in losses.  The estimated loss ratio is less than 10% in most areas affected by scenario earthquake ground motions.  However, in some cases, loss ratio exceeds 10% in the vicinity of the rupturing fault.  For the three most damaging earthquakes on the Northern San Andreas fault segments, loss ratio as high as 50% was estimated for some census tracts in northeast San Mateo County.  In Southern California, the most damaging scenario is the M7.1 earthquake on the Puente Hills fault.  With building loss ratios up to 30% in some census tracts, total predicted building loss is $79 billion ($82.8 billion in total economic loss).  HAZUS calculations suggest that the earthquake would kill 500 to 2000 people and displace 58-thousand households.  The calculations show at least moderate damage to 569 highway bridges, 2 airports and over 470-thousand buildings.  These numbers are in the lower range of an earlier estimate by Field and others for the same fault (2005, Earthquake Spectra).  Other notable high loss scenarios for Southern California are: an M6.9 earthquake on the Newport-Inglewood fault with over $34 billion in total building loss, an M7.1 earthquake on the Palos-Verde Fault with over $20 billion in total building loss and an M7.8 rupture along the Southern San Andreas Fault with over $20 billion in total building loss.  When the same scenario was studied in detail in the 2008 ShakeOut Scenario, the total building loss was higher at $35 billion.  This is likely due to a more detailed building inventory and ground failure effects (liquefaction, landslides, and surface rupture).

 

Table 1. Top Five Most Damaging Scenarios Earthquakes in Northern and Southern California and Associated Economic Losses

 

 

 

Economic Losses ($M)

Scenario Earthquakes

M

Buildings Related

Transportation System

Utility System

 Northern California

N1

 Northern San Andreas Fault

7.90

79,834

1,436

2,583

 (SAS+SAP+SAN+SAO)1

N2

 Northern San Andreas Fault

7.76

70,628

1,172

2,026

 (SAS+SAP+SAN)1

N3

 Northern San Andreas Fault 

7.83

66,216

1,162

1,856

 (SAP+SAN+SAO)1

N15 

 Hayward-Rodgers Creek Fault

7.26

36,883

826

1,695

 (HS+HN+RC)1

N4

 Northern San Andreas Fault

7.42

34,299

721

1,212

 (SAF_SAS+SAP)1

 Southern California

S8

 Puente Hills Fault

7.1

79,662

1178

1,966

S17

 Newport – Inglewood Fault

6.9

34,319

482

958

S1

 Verdugo Fault

6.7

23,751

270

826

S2

 San Andreas Fault – Southern

7.8

20,515

503

1,489

S18

 Palos Verdes Fault

7.1

20,084

367

796

1These are section abbreviations. Click here to see full names.

 

There are significant and consistent differences in the estimated building related losses for the UCERF 2-based scenarios and for USGS scenarios (figure 2, for example).  Among the ten UCERF 2-based scenarios, six can be compared directly to the corresponding USGS scenarios (similar earthquake magnitude and fault model).  Comparison shows that the estimated building-related loss for a UCERF 2-based scenario is 28% to 63% lower than that for the comparable USGS scenario (Table 2).  This difference is mainly due to different GMPEs used in the UCERF 2-based scenarios and in USGS scenarios.  

 

Figure 2. Distribution of percent loss, calculated as the ratio of economic loss due to building damage to building replacement value times 100, for each census tract.

 

Table 2. Comparison of Estimated Building Losses for UCERF 2-based Scenarios and USGS Scenarios

 

Scenario Earthquakes

UCERF 2-Based Scenario

Comparable USGS Scenario

Difference

M

Building Related Loss ($M)

M

Building-Related Loss ($M)

(%)

Southern San Andreas Fault (CO)1,2

6.95

684

7.1

5,138

-87

San Jacinto Fault (SBV+SJV+A+C)1

7.76

10,983

No comparable scenario

San Jacinto Fault (A+C)

7.49

2,654

Hayward-Rodgers Creek Fault

(RC+HN+HS)1

7.29

21,966

7.26

36,883

-40

Hayward-Rodgers Creek Fault (RC)1

6.98

3,963

6.98

6,582

-40

Northern San Andreas Fault

(SAO+SAN+SAP+SAS)1

7.99

29,412

7.9

79,834

-63

Northern San Andreas Fault

(SAP+SAS)1

7.47

17,031

7.42

34,299

-50

Imperial

6.9

236

7

421

-44

Palos Verdes

7.2

14,513

7.1

20,084

-28

Newport-Inglewood3

7.2

42,980

6.9

34.319

25

1These are section abbreviations. Click here to see full names.
2The lower UCERF 2 magnitude for this scenario may have contributed to greater difference in estimated loss.
3For this scenario, UCERF 2 used larger magnitude and included rupture along the Rose Canyon Fault.

 

Most of the scenario ShakeMaps used in the CGS 2005 study are identical to the ones used in the 2009 study for USGS scenarios.  Therefore, for a given common ShakeMap scenario, comparison of loss estimates from the 2009 study and from the CGS 2005 study reflects differences in the HAZUS default inventory information on built environment and demographics and in HAZUS analytical models.  Comparison is made for building-related losses only because the CGS 2005 study only reported building-related losses.  In Northern California, 20 of the 33 comparable scenarios show building related losses from the 2009 study that are within 10% of 2005 estimates.  For most of the scenarios on the Northern San Andreas Fault, the 2009 estimates are up to 40% higher than the 2005 estimates.  In contrast, the 2009 estimates are up to 36% lower than the 2005 estimates for most other USGS scenarios.  In Southern California, 75% of the common scenarios result in lower building related loss when estimated from 2009 study compared with the 2005 study. Half of the differences are between 30% and 71% (see more details).

Uncertainties are inherent in HAZUS loss estimates, just as they are inherent in all other hazard, risk, and loss estimate methodologies.  Uncertainties arise from incomplete scientific knowledge concerning earthquake occurrence and ground motion characteristics and their effects on buildings and other facilities.  They also result from incomplete or inaccurate inventories of the built environment, demographics, and economic parameters.  A third source of uncertainties comes from the approximations and simplifications that are necessary for model analyses.  It is estimated that these factors can result in total uncertainties in loss estimates produced by the HAZUS-MH Earthquake Model of up to a factor of two or more (FEMA, 2009). 

Conclusions

  • Three of the four most damaging USGS scenarios involve co-seismic rupture of different combinations of the Northern San Andreas Fault segments. The second most damaging scenario is the rupture of the Puente Hills Fault, a blind-thrust fault directly beneath Los Angeles. This scenario has been studied in greater detail by Field et al. (2005, Earthquake Spectra).
  • Building related losses estimated using NGA GMPEs are 28% – 63% lower than those using ShakeMap ground motions in six comparable scenarios analyzed. Realistic loss estimation depends on accurate prediction of ground motions. Additional scenarios should be analyzed to evaluate further the implication of NGA models on loss estimation.
  • Comparison of estimated building related losses for the USGS scenarios from the 2009 study to those from the CGS 2005 study shows no consistent trend that could be attributed to changes in HAZUS methodology.

CGS is in the process of estimating annualized losses based on the 2008 update of the seismic hazard maps.


A complete set of selected HAZUS results for all the scenarios analyzed in the 2009 study can be found in Appendix A of the project report (download).  For each scenario, the results include:

Maps

·         Shaking intensity map (USGS ShakeMap)

·         Peak ground acceleration by census tract (HAZUS map)

·         Total building loss by census tract (HAZUS map)

·         Loss ratio by census tract [ratio of building damage (includes structural damage and non-structural damage) to replacement value (exposed value of buildings)]

·         Displaced households by census tract (HAZUS map)

·         Debris generated by census tract (HAZUS map)

 

Tables

·         Dam inventory and ground motions at dam locations

·         Direct economic loss for buildings by county

·         Short term shelter needs by county

·         Casualties summary report by county

 

Other Summary Reports

·         Global Summary Report

·         Quick assessment reports

 

These results may also be viewed by clicking the scenario names in table 3 for Northern California, table 4 for Southern California, and table 5 for UCERF 2-based scenarios.  Scenario earthquakes are listed by the abbreviations of fault and fault section names. Click here to see the full names.

Table 3. Northern California Scenario Earthquakes and Associated Economic Losses

 

 

Scenario Earthquakes

 

M

Economic Losses ($M)

Buildings Related

Transportation System

Utility System

N1

SAF_SAS+SAP+SAN+SAO

7.90

79,834

1,436

2,583

N2

SAF_SAS+SAP+SAN

7.76

70,628

1,172

2,026

N3

SAF_SAP+SAN+SAO

7.83

66,216

1,162

1,856

N4

SAF_SAS+SAP

7.42

34,299

721

1,212

N5

SAF_SAS

7.03

6,789

118

353

N6

SAF_SAP

7.15

24,788

472

845

N7

SAF_SAN+SAO

7.70

17,814

426

910

N8

SAF_SAN

7.45

11,474

344

798

N9

SAF_SAO

7.29

161

32

100

N10

HRC_HS

6.67

14,469

221

613

N11

HRC_HN

6.49

7,655

180

518

N12

HRC_HS+HN

6.91

22,660

426

983

N13

HRC_RC

6.98

6,582

153

572

N14

HRC_HN+RC

7.11

19,244

508

1,163

N15

HRC_HS+HN+RC

7.26

36,883

826

1,695

N16

CLV_CS

5.78

168

12

23

N17

CLV_CC

6.23

2,666

45

135

N18

CLV_CS+CC

6.36

3,422

52

153

N19

CLV_CN

6.78

10,176

137

433

N20

CLV_CC+CN

6.90

13,534

182

528

N21

CLV_CS+CC+CN

6.93

14,217

196

540

N22

CGV_CON

6.25

2,644

76

288

N23

CGV_GVS

6.24

1,872

78

280

N24

CGV_CON+GVS

6.58

 5,326

122

455

N25

CGV_GVN

6.02

528

48

115

N26

CGV_GVS+GVN

6.48

2,267

96

351

N27

CGV_CON+GVS+GVN

6.71

6,631

144

513

N28

SGF_SGS

7.0

963

19

80

N29

SGF_SGN

7.2

12,111

274

567

N30

SGF_SGS+SGN

7.4

15,005

361

742

N31

GNV_GS

6.6

1,752

59

191

N32

GNV_GN

6.7

3,198

79

319

N33

GNV_GS+GN

6.9

5,175

109

439

N34

MTD

6.65

7,296

118

472

N35

GV

?

3,503

111

513

 

Table 4.  Southern California Scenario Earthquakes and Associated Economic Losses

 

 

 

Economic Losses ($M)

Scenario Earthquakes

M

Buildings Related

Transportation System

Utility System

S1

Verdugo Fault

6.7

23,751

270

826

S2

San Andreas Fault – Southern M7.8

7.8

20,515

503

1,489

S3

Chino Hills Fault

6.7

11,390

104

554

S4

San Joce -Carro Prieto Fault

7

267

17

213

S5

Hosgri Fault

7.5

1,020

47

232

S6

Elsinore Fault (Julian)

7.1

1,184

51

129

S7

North Channel Slope

7.4

5,814

140

553

S8

Puente Hills Fault

7.1

79,662

1178

1,966

S9

San Joaquin Hills Fault

6.6

16,557

165

482

S10

Elsinore Fault

6.8

2,481

64

190

S11

Raymond Fault

6.5

16,495

158

587

S12

Whittier Fault

6.8

15,965

155

649

S13

Imperial Valley Fault

7

421

37

341

S14

San Andreas Fault – Coachella Valley

7.1

5,138

152

287

S15

San Andreas Fault – Southern M7.4

7.4

9,138

279

897

S16

San Jacinto Fault

6.7

4,366

89

328

S17

Newport – Inglewood Fault

6.9

34,319

482

958

S18

Palos Verdes Fault

7.1

20,084

367

796

S19

Santa Monica Fault

6.6

16,308

99

490

S20

Rose Canyon Fault

6.9

9,771

183

456

S21

San Andreas Fault – 1857

7.8

12,586

367

1,257

 

Table 5. UCERF 2-Based Scenario Earthquake and Associated Economic Losses

 

 

Scenario Earthquakes

 

M

Economic Losses ($M)

Buildings Related

Transportation System

Utility System

U1

SAF_CO

6.95

684

3

163

U2

SJ_SBV+SJV+A+C

7.76

10,983

224

798

U3

SJ_A+C

7.49

2,654

69

302

U4

HRC_RC+HN+HS

7.29

21,966

404

1,136

U5

HRC_RC

6.98

3,963

93

424

U6

SAF_SAO+SAN+SAP+SAS

7.99

29,412

503

1,857

U7

SAF_SAP+SAS

7.47

17,031

303

738

U8

Imperial

6.9

236

18

274

U9

Palos Verdes

7.2

14,513

324

782

U10

Newport-Inglewood

7.2

42,980

671

1,679