Geoscience Society of New Zealand Hochstetter Lecture Presented by: Russ Van Dissen (on behalf of the It s Our Fault team)

Transcription

1 Geoscience Society of New Zealand Hochstetter Lecture 2011 Presented by: Russ Van Dissen (on behalf of the It s Our Fault team)

2 It s Our Fault Major Sponsors A multi-year applied research project funded by New Zealand s Earthquake Commission Accident Compensation Corporation Wellington City Council Greater Wellington Wellington Region Civil Defence Emergency Management Group Natural Hazards Research Platform NHRP

3 It s Our Fault The Goal To see Wellington positioned to become a more resilient city through a comprehensive study of the likelihood of large Wellington earthquakes, the effects of these earthquakes, and their impacts on humans and the built environment NHRP

4 It s Our Fault Likelihood team Geological Investigations R. Van Dissen, K. Clark, U. Cochran, M. Hemphill-Haley, R. Langridge, N. Litchfield, N. Pondard, W. Ries, H. Seebeck, P. Villamor P. Barnes, G. Lamarche, J. Mountjoy T. Little, R. Carne, D. Ninis, U. Rieser, E. Schermer, E. Smith Wellington Geodetic & GPS Studies L. Wallace, J. Beavan, N. Palmer Synthetic Seismicity Modelling R. Robinson, N. Litchfield, R. Van Dissen Wellington Fault Conditional Probability of Rupture D. Rhoades, R. Langridge, R. Robinson, R. Van Dissen T. Little, D. Ninis, E. Smith Project Facilitation H. Brackley, K. Berryman, A. King, T. Webb

5 It s Our Fault Effects team Geological & Geotechnical Characterisation G. Dellow, P. Barker, B. Fry, B. Lukovic, G. McVerry, N. Perrin, M. Rattenbury, B. Stephenson, R. Van Dissen S. Semmens D. Boon Geophysical Parameterisation B. Fry, P. Barker, R. Benites, B. Stephenson Subduction Interface Earthquake Motions C. Francois-Holden, G. McVerry, J. Zhao Liquefaction G. Dellow, R. Beetham, N. Perrin, S. Read S. Semmens Ground Motion Modelling C. Francois-Holden, R. Benites, G. Dellow, B. Fry, A. Kaiser, G. McVerry, J. Zhao Project Facilitation H. Brackley, K. Berryman, A. King, R. Van Dissen, T. Webb

6 It s Our Fault Impacts team Engineering Stream J. Cousins, R. Buxton, G. Dellow, C. Francois-Holden, A. King, G. McVerry, N. Pondard, W. Smith Social Science Stream D. Johnston, J. Becker, W. Saunders, K. Wright Project Facilitation H. Brackley, R. Van Dissen, T. Webb, A. King, K. Berryman

7 Wellington s Earthquake Setting

8 Wellington s Earthquake Setting (Pondard & Barnes, JGR; & NZ Active Faults Database)

9 Wellington s Earthquake Setting Wairarapa Fault Ohariu Fault Wellington Fault Photograph by: Lloyd Homer

10 New Zealand s Tectonic Setting Australian Plate Pacific Plate A cricket pitch of displacement every 500 years

11 (GeoNet) New Zealand Shallow Seismicity Depths < 40 km (a ten year snap-shot) New Zealand Deep Seismicity Depths 40 km (a ten year snap-shot)

12 Large Historical Earthquakes Largest historical earthquake 1855, Mag ~8.2

13 (NZ Active Faults Database) New Zealand s Active faults

14 Time averaged general hazard From: Stirling et al., accepted, National seismic hazard model for New Zealand: 2010 update. Bulletin of the Seismological Society of America.

15 A more specific question Which faults contribute most to losses?

16 Likely Losses ($b) It s Our Fault motivation (an example) 6 Damage to NZ Houses in earthquakes Year (Figure courtesy of W Smith, GNS Science)

17 Likely Losses ($b) It s Our Fault motivation (an example) 6 Damage to NZ Houses Wellington region faults Other sources Year (Figure courtesy of W Smith, GNS Science)

18 Importance of characterising Likelihood Relative contribution to loss by specific faults

19 Importance of characterising Likelihood Relative contribution to loss by specific faults But how much did we actually know about earthquake timing on the Wellington Fault?

20 It s Our Fault Wellington Fault Knowledge Prior to It s Our Fault 2 nd rupture Most recent rupture Limited knowledge made it difficult to estimate timing of next rupture

21 It s Our Fault Wellington Fault Possible new knowledge scenarios

22 It s Our Fault Wellington Fault Possible new knowledge scenarios So, which scenario is most correct?

23 It s Our Fault - Likelihood Phase Geological Investigations Wellington Fault paleoearthquake characterization (Langridge et al. BSSA) Wellington Fault single-event displacement characterization (Little et al. JGR) Wellington Fault slip-rate characterization (Ninis et al.) Wairarapa Fault paleoearthquake characterization (Little et al. Lithosphere) Wairarapa Fault slip-rate characterization (Carne et al. NZJGG; Villamor et al.) Ohariu Fault paleoearthquake characterization (Litchfield et al. NZJGG) Detailed mapping offshore Cook Strait faults (Pondard & Barnes JGR) Past Subduction Zone ruptures (Clark et al. NZJGG; Clark & Cochran) Wellington Geodetic & GPS Studies (Wallace et al. JRG) Synthetic Seismicity Modelling (Robinson et al. GJI ) Wellington Fault Conditional Probability of Rupture (Rhoades et al. BNZSEE)

24 It s Our Fault study sites & fault map (Pondard & Barnes, JGR; & NZ Active Faults Data Base) Select It s Our Fault study sites

25 Wellington Fault IOF Investigation Sites TK-LG EH-TM (Langridge et al. BSSA) (Little et al. JGR) (Ninis et al.) Photograph by: Lloyd Homer K

26 (Langridge et al. BSSA) Wellington Fault Te Kopahou site southern end of Wellington-Hutt Valley segment shutter ridge site enclosed swampy basin offset stream of c. 47 metres 2 trenches excavated

27 Wellington Fault Te Kopahou site (Langridge et al. BSSA)

28 (Langridge et al. BSSA) Wellington Fault - Te Kopahou trench 1 Rupture history of Wellington Fault extended by 4 3 ruptures within last ~2,300 years Rupture history now overlaps in time with that of Wairarapa Fault rupture history

29 (Langridge et al. BSSA) Wellington Fault - Te Kopahou trench 1 Rupture history of Wellington Fault extended by 4 3 ruptures within last ~2,300 years Rupture history now overlaps in time with that of Wairarapa Fault rupture history First Rupture

30 (Langridge et al. BSSA) Wellington Fault - Te Kopahou trench 1 Rupture history of Wellington Fault extended by 4 3 ruptures within last ~2,300 years Rupture history now overlaps in time with that of Wairarapa Fault rupture history Interseismic period

31 (Langridge et al. BSSA) Wellington Fault - Te Kopahou trench 1 Rupture history of Wellington Fault extended by 4 3 ruptures within last ~2,300 years Rupture history now overlaps in time with that of Wairarapa Fault rupture history Second Rupture

32 (Langridge et al. BSSA) Wellington Fault - Te Kopahou trench 1 Rupture history of Wellington Fault extended by 4 3 ruptures within last ~2,300 years Rupture history now overlaps in time with that of Wairarapa Fault rupture history Interseismic period

33 (Langridge et al. BSSA) Wellington Fault - Te Kopahou trench 1 Rupture history of Wellington Fault extended by 4 3 ruptures within last ~2,300 years Rupture history now overlaps in time with that of Wairarapa Fault rupture history Third Rupture

34 (Langridge et al. BSSA) Wellington Fault - Te Kopahou trench 1 Rupture history of Wellington Fault extended by 4 3 ruptures within last ~2,300 years Rupture history now overlaps in time with that of Wairarapa Fault rupture history Interseismic period

35 (Langridge et al. BSSA) Wellington Fault - Te Kopahou trench 1 Rupture history of Wellington Fault extended by 4 3 ruptures within last ~2,300 years Rupture history now overlaps in time with that of Wairarapa Fault rupture history Fourth Rupture

36 (Langridge et al. BSSA) Wellington Fault - Te Kopahou trench 1 Rupture history of Wellington Fault extended by 4 3 ruptures within last ~2,300 years Rupture history now overlaps in time with that of Wairarapa Fault rupture history Interseismic period

37 (Langridge et al. BSSA) Rupture Timing timing of most recent rupture & timing of older rupture events Datum is AD 2010

38 (Langridge et al. BSSA) Rupture Timing timing of most recent rupture & timing of older rupture events Timing of most recent rupture is slightly younger than previously thought Inter-event times between ruptures are longer than previously suspected Datum is AD 2010

39 Rupture Timing Comparisons Wairarapa Fault Wellington Fault Ohariu Fault Wairau Fault (Barnes & Pondard G 3 ; Langridge et al. BSSA; Litchfield et al. NZJGG; Little et al. JGR )

40 Wellington Fault Te Marua Site Photographs by: Lloyd Homer

41 size of single-event displacements Young River Terraces at Te Marua Photograph by: Lloyd Homer Important site previous single-event estimate at site: (last EQ only) was 4.2 ± 0.5 m (Little et al. JGR)

42 RTK-GPS Topographical Survey (east part) Landforms on this image are all dextrally displaced by ~20 m n = 21,848 points (Little et al. JGR)

43 Summary of Displacements 9.7 ± 1.6 m (Little et al. JGR)

44 Summary of Displacements 4 Single-Event Displacements Last EQ 9.7 ± 1.6 m EQ 4 Mean Single-Event Displacement 5.0 ± 1.5 m (1 RMS scatter of slips about the mean) Penult. EQ EQ 3 This mean per-event slip is ~20% higher than previous estimate of singleevent slip on Wellington Fault (Little et al. JGR)

45 Summary of Displacements Last EQ 9.7 ± 1.6 m EQ 4 Emerald Hill and Possibly a Fifth Single-Event Displacement At Emerald Hill EQ 5? EQ 3 Penult. EQ (Little et al. JGR)

46 Wellington Fault slip rate - offset terraces at Te Marua (Ninis et al.)

47 Wellington Fault slip rate - offset terraces at Te Marua (Ninis et al.)

48 Terrace riser projections Terrace risers are piercing points from which we can determine displacement Birchville Park Terrace Birchville Park Terrace (Ninis et al.)

49 Slip rate results Average Wellington Fault Holocene slip rate of ~5.8 ± 0.7 mm/yr Period of heightened surfacerupture activity in the early Holocene Followed by a period of relative quiescence Then ~4 surface ruptures in the last ~4 ka (Langridge et al. BSSA) (Ninis et al.)

50 Wellington s Earthquake Setting

51 GPS Survey Campaign

52 GPS Velocities

53 (Wallace et al. JGR) Modelling GPS Data Jointly invert: 1) GPS velocities & 2) Active fault slip rate and location data Solve for: 1) Poles of rotation of tectonic blocks & 2) Degree of interseismic coupling on faults in the region (including subduction interface)

54 (Wallace et al. JGR) Results of best-fit model

55 (Wallace et al. JGR ) Slip Deficit on the Subduction interface

56 (Wallace et al. JGR ) Slip Deficit on the Subduction interface Possible subduction rupture source area(s)

57 Fault Interactions Synthetic Seismicity Modelling (Pondard & Barnes JGR) When one tugs at a single thing in nature, he finds it attached to the rest of the world. John Muir

58 Fault Interactions Synthetic Seismicity Modelling (Pondard & Barnes JGR) When one tugs at a single thing in nature, he finds it attached to the rest of the world. John Muir

59 Synthetic Seismicity Modelling Fault Interaction Investigations Effect of fault rupture on other nearby faults 1855 earthquake de-stressed Wellington & Ohariu faults

60 How it was modelled 15 years ago Seven faults with very simplified geometries (Robinson & Benites JGR 1996)

61 Fault Interaction model Large region to encompass Wellington and Wairarapa faults Over 50 large faults with realistic geometries, and 3000 randomly placed small faults (Robinson et al. GJI)

62 (Robinson et al. GJI) Subduction interface

63 Cumulative moment release vs. time (for time period 55,000-56,000 years) yrs (Robinson et al. GJI)

64 Cumulative moment release vs. time (for time period 55,000-56,000 years) yrs Times to build resilience (Robinson et al. GJI)

65 Cumulative moment release vs. time (for time period 55,000-56,000 years) Times when you wish you had yrs (Robinson et al. GJI)

66 Individual modelled recurrence times for large ruptures of the Wellington Fault (Robinson et al. GJI)

67 Wellington-Wairarapa fault-pair rupture statistics Wellington Fault rupture (Robinson et al. GJI)

68 Wellington-Wairarapa fault-pair rupture statistics Mag >7.3 Wairarapa Fault rupture lengthens time between large Wellington Fault ruptures (Robinson et al. GJI)

69 Wellington-Wairarapa fault-pair rupture statistics Mag Same is true for moderate sized Wellington Fault earthquakes too (Robinson et al. GJI)

70 It s Our Fault Wellington Fault data Current knowledge, after It s Our Fault Event 4 Event 3 Event 2 Event 1

71 It s Our Fault Wellington Fault data Current knowledge, after It s Our Fault Event 4 Event 3 Event 2 Event 1 Less frequent Wellington Fault ruptures plus a recent Wairarapa Fault rupture pushes probability of next Wellington Fault rupture out into the future

72 It s Our Fault Wellington Fault data Current knowledge, after It s Our Fault Event 4 Event 3 Event 2 Event 1 Less frequent Wellington Fault ruptures plus a recent Wairarapa But, Fault by rupture how pushes much? probability of next Wellington Fault rupture out into the future

73 Wellington Fault Conditional Probability of Rupture Calculate conditional probability of rupture of the Wellington Fault, accounting for all relevant parameter and data uncertainties, and encompassing: new and existing earthquake geology data relating to: elapsed time since most recent rupture, timing of older ruptures, single event displacement size, and slip rate rupture statistics of the Wellington-Wairarapa fault pair in a synthetic earthquake catalogue derived from a physics-based numerical model various recurrence-time models (Rhoades et al. BNZSEE)

74 Methodology Rhoades, D.A., Van Dissen, R.J., Dowrick, D.J., 1994, On the handling of uncertainties in estimating the hazard of rupture on a fault segment. Journal of Geophysical Research 99: 13,701-13,712. Rhoades, D.A., Van Dissen, R.J., 2003, Estimates of the time-varying hazard of rupture of the Alpine Fault, New Zealand, allowing for uncertainties. New Zealand Journal of Geology & Geophysics 46: Rhoades, D.A., Stirling, M.W., Schweig, E., Van Dissen, R.J., 2004, Time-varying earthquake hazard in the Wellington region. Institute of Geological & Nuclear Sciences Client Report 2004/141 (prepared for the Earthquake Commission). allows hazard (probability of rupture) to be expressed as a single value that accounts for both data and parameter uncertainties

75 Wellington-Hutt Valley segment of the Wellington Fault

76 Input data timing of most recent rupture & timing of older rupture events Datum is AD 2010 (Langridge et al. BSSA)

77 Input data size of single-event displacements; m (based on the last 4 surface ruptures at Te Marua) Holocene dextral slip-rate; 5.8 ± ~0.7 mm/yr (Little et al. JGR) Slip rate and uncertainty is explicitly derived from Birchville Park terrace displacement and age distributions listed below. Displacement: triangular distribution /-12 m (at ~99% confidence) Age: normal distribution 9.37 ± 0.61 ka (at 1σ uncertainty) (Ninis et al.)

78 Input info Rupture statistics of the Wellington-Wairarapa fault-pair Wairarapa/Awatere bias (dts with vs dts without) = 90 to 270 yr (preferred = +260 yr) Wairarapa/Awatere bias (dts with vs all dts) = ~+65 yrs (Robinson et al. GJI ) (Note: all dts greater than 2 ka are plotted at 2 ka)

79 Recurrence Time Models Exponential Weibull Weibull Log-normal Inverse Gaussian Inverse Gaussian Log-normal Exponential Time (normalised to recurrence interval)

80 Wellington Fault estimated probability of rupture in 100 years Recurrence-time distribution 100 year probability % change from previous estimate Exponential 10% ~ 40% reduction Lognormal 12% ~ 70% reduction Weibull 11% ~ 60% reduction Inverse Gaussian 11% ~ 60% reduction (Rhoades et al. BNZSEE) (Rhoades et al. 2004)

81 One way of looking at new Wellington Fault results

82 (image by D. D Cruz) Another way of looking at it Probability of rupture of Wellington Fault within next 100 years Pre-It s Our Fault: ~ 30% New: ~ 10%

83 Sensitivity runs Favour the older end of the age range of the most recent event Exclusion of occurrence of a more speculative Event 5 Higher coefficient of variation of single-event displacement (0.57 cf. 0.30) Elevated and reduced slip rate (Rhoades et al. BNZSEE)

84 (Rhoades et al. BNZSEE)

85 Sensitivity runs Black = preferred Red = 1855 effect Green = increased CoV of SED Blue = reduced slip rate Orange = elevated slip rate (Rhoades et al. BNZSEE)

86 (image by D. D Cruz) after sensitivity runs, still looks like this Probability of rupture of Wellington Fault within next 100 years Pre-It s Our Fault: ~ 30% New: ~ 10%

87

88 It s Our Fault some key likelihood conclusions Significant reduction in the likelihood of rupture of the Wellington Fault over the next hundred years, or so. This is Good. However, no room for complacency as there are other earthquake sources in, and around, the region that can produce significant damage and loss. This highlights the need, and benefits, of continued pursuit of resilience.

89 More than a few large earthquake sources in and around Wellington

90 More than a few large earthquake sources in and around Wellington

91 The Wellington Fault Parting Shot The Region

92 Conditional probability of ruputre of the Ohariu Fault & Wairarapa Fault

93 Results Comparison of hazard of rupture over the next 100 years for the: Wellington Fault (blue) Wairarapa Fault (red) Ohariu Fault (yellow)

94 It s Our Fault - Effects Phase Geological, Geotechnical, and NZS 1170 Subsoil Characterisation Wellington City CBD (Semmens et al. PCEE) Lower Hutt (Boon et al. PCEE) Wider area including Porirua & Kapiti Coast (Dellow et al.) Ground motion site effects terms as a continuous function of site period and V s 30 (McVerry et al. PCEE) Seismic instrumentation and inversion for physical parameters of Wellington and the Hutt Valley (Fry et al.) Probabilistic Liquefaction Hazard Assessment (Dellow et al.) Subduction Zone Ground Motion Simulations (Holden & Zhao PCEE) Comparison of Ground Motion Modelling Techniques (Kaiser et al.)

95 3D Geological & Geotechnical Characterisation of Central Wellington (Semmens et al. PCEE)

96 Thorndon overbridge Central Wellington Study Area Greywacke Rock Shallow Soil Very Soft Soil Deep/Soft Soil (Semmens et al., 2010) Wellington Fault Greywacke Rock Wellington Hospital

97 Project objectives 3D Geological model for central Wellington Derivative Maps Surficial geological Depth to bedrock Site period V s 30 Subsoil class (based on NZS 1170) (Semmens et al. PCEE)

98 Inputs 1025 Boreholes Microtremor sites shear-wave velocities low amplitude natural period unit thicknesses Databases Databases have been compiled that include: lithology (as recorded on log) geotechnical properties SPT N count shear-wave velocity model lithology Data available via GNS PetLab ( (Semmens et al. PCEE)

99 Inputs 1025 Boreholes Microtremor sites shear-wave velocities low amplitude natural period unit thicknesses Databases Databases have been compiled that include: lithology (as recorded on log) geotechnical properties SPT N count IOF, ~1800 Wellington & Hutt Valley drill-hole records shear-wave velocity DEVORA, ~2200 Auckland drill-hole records model lithology Data available via GNS PetLab ( Geotechnical database of NZ rock and soil properties (Semmens et al. PCEE)

100 Data Modelling Each layer in a borehole was assigned one of 17 units based on: grain size, SPT N count, weathering condition & depositional setting The 17 units were then assigned to one of four larger groups and were successfully modelled: Hydraulic Fill Loose/Soft Deposits Stiff/Hard Deposits Greywacke Sandstone/Mudstone Bedrock (Semmens et al. PCEE)

101 Data Modelling

102 V s summary for Wellington City (Boon et al. PCEE; Fry et al.; Semmens et al. PCEE)

103 (Semmens et al. PCEE)

104 Results Geological Map (1:5000 scale) Map units include: greywacke alluvium colluvium marginal marine deposits swamp deposits Compiled using: boreholes test pits existing maps limited field mapping (Semmens et al. PCEE)

105 Results Depth to Bedrock (red contours are at 50 m intervals) (Semmens et al. PCEE)

106 Subsoil Class Old-fashioned microzoning for earthquake effects (as in 1974 & 1992) Assessment of relative earthquake hazard components (e.g. shaking amplification, landslide, liquefaction) Simple, qualitative, designation for amplification potential (e.g. high-medium-low) Perhaps useful for urban planning, but not much use for engineering design

107 Subsoil Class NZS 1170 The Structural Design Standard for New Zealand Attempts to quantify the shaking amplification across differing subsoil classes (i.e. near surface ground conditions), and prescribes design actions Defines subsoil classes and methods to establish them Fundamental components in determining subsoil class include: natural period & shear wave velocity

108 NZS 1170 Subsoil Class Definitions: Subsoil Class Class: Description: Definition: A Strong Rock UCS > 50MPa...& V s 30m > 1500m/s...& Not underlain by <18MPa or V s 600m/s materials B Rock 1< UCS <50MPa...& V s 30m >360 m/s...& Not underlain by UCS< 0.8MPa or V s 300m/s materials A surface layer no more than 3m depth (HW-CW rock/soil) C Shallow Soil Not class A, B or E Low Amplitude Natural Period 0.6s, or Have depths of soils not exceeding those in Table 2 D Deep or Soft Soil Not class A, B or E Low Amplitude Natural Period > 0.6s, or Have depths of soils exceeding those in Table 2, or Underlain by < 10m soils with undrained shear strength < 12.5 KPa or SPT N < 6 E Very Soft Soil > 10m soils with undrained shear strength < 12.5 KPa or SPT N < 6 or Vs 150m/s or >10m combined (previous)

109 NZS 1170 Subsoil Class Definitions: Subsoil Class Class: Description: Definition: A Strong Rock UCS > 50MPa...& V s 30m > 1500m/s...& Not underlain by <18MPa or V s 600m/s materials B Rock 1< UCS <50MPa...& V s 30m >360 m/s...& Not underlain by UCS< 0.8MPa or V s 300m/s materials A surface layer no more than 3m depth (HW-CW rock/soil) C Shallow Soil Not class A, B or E Low Amplitude Natural Period 0.6s, or Have depths of soils not exceeding those in Table 2 D Deep or Soft Soil Not class A, B or E Low Amplitude Natural Period > 0.6s, or Have depths of soils exceeding those in Table 2, or Underlain by < 10m soils with undrained shear strength < 12.5 KPa or SPT N < 6 E Very Soft Soil > 10m soils with undrained shear strength < 12.5 KPa or SPT N < 6 or Vs 150m/s or >10m combined (previous)

110 Results (contour interval = 0.2s; red contour is 0.6s) Based on: Site Period Modelled 3D distribution of geological units Hydraulic Fill Loose/Soft Deposits Stiff/Hard Deposits Bedrock V s determinations for these units 4 shear-wave velocity travel time Ground-truthed against known, but limited, site period determinations (Semmens et al. PCEE)

111 Spectral Shape Factor Subsoil Class B Map + NZS 1170 = a directly applicable microzonation C D 3.5 NZS1170 Spectral Shape Factors D D C B Class A/B Rock Class C Shallow Soil Class D Deep or Soft Soil B C (Semmens et al. PCEE; McVerry PCEE) Period T(s)

112 3D Geological & Geotechnical Characterisation of the Hutt Valley (Boon et al. PCEE)

113 Data sources & distribution DTM Geological Mapping 1: : Borehole data Hutt Valley database (n = ~825) Geophysical investigations Gravity Seismic Microtremor (Boon et al. PCEE)

114 (Boon et al. PCEE) Distribution of geological materials

115 Depth to Bedrock (Boon et al. PCEE)

116 (Boon et al. PCEE) Site Period 0.6 s 1.0 s 1.5 s

117 (Boon et al. PCEE) Subsoil Class (NZS ) D C B

118 Site-effect terms as continuous functions of site period (McVerry PCEE)

119 Spectral Shape Factor Motivation B NZS 1170 site-class based spectral shape factors have large jumps at site-class boundaries (especially between Classes C & D) D Often difficult to determine whether borderline sites are Class C or Class D, with 60% penalty for Class D C 3.5 NZS1170 Spectral Shape Factors D D C B C Class A/B Rock Class C Shallow Soil Class D Deep or Soft Soil B (McVerry PCEE) Period T(s)

120 Spectral Shape Factor Aims B Develop new site-effect terms for NZS 1170 that are continuous functions of site parameters D Alleviate large jumps in loadings and costs between site-classes C & D C 3.5 NZS1170 Spectral Shape Factors D D C B C Class A/B Rock Class C Shallow Soil Class D Deep or Soft Soil B (McVerry PCEE) Period T(s)

121 Approach NZS 1170 spectral shape factors were derived using McVerry et al. NZ response spectrum ground-motion model (excludes Class E Very Soft Soil sites) Replace site-class based site-effect terms of McVerry et al. model with terms that are continuous functions of site parameters, by reanalysing same strong-motion dataset Carry through results from modified ground-motion model to revised spectral shapes for NZS 1170 (McVerry PCEE)

122 Site parameters Site period Tsite obvious candidate NZS 1170 classes based on this parameter can estimate using NZS 1170 procedures Also considered V s 30, depth & Vave (average shear-wave velocity to rock) as alternative site parameters both singly, and for velocity parameters in combination with Tsite or depth Compiled these parameters for all sites throughout NZ that were used to develop current NZ response spectrum attenuation model of McVerry et al. Used data from throughout NZ to develop model (McVerry PCEE)

123 Proposed site-effect terms ln SA( T) ln SA rock ( T) ISE( T, site _ parameters ) INONLIN ( T, SA rock ( T)) ISEtype ISE INONLINtype INONLIN 0 (site class model) C 29 (T)δC + C 43 (T)δD δc=1 for Class C, else 0 δd=1 for Class D, else 0 0 (linear) 0 1 (site-period) C 48 (T) + C 49 (T) T site 1 C 51 (T) ln (SA B (T) ) 4 (V s30 ) C 48 (T) + C 49 (T) ln(v s30 ) 2 [C 51 (T) + C 52 (T) T site ]* ln(sa B (T) ) Model Code Description S0N0,S0N1 Site class based: N0 linear, N1 nonlinear (as in McVerry et al., 2006) S1N0, S0N2 S4N0 Site-period based: N0 linear, N2 site-period dependent nonlinear term Vs30-based, linear Other forms and site parameters also considered, but not discussed here (McVerry PCEE)

124 AIC difference Top curve = best model at that spectral period 20 S0N1-site class, nonlinear AIC(S0N1)-AIC(Alternative Model) Positive AIC difference = Improved model S0N0 - site class, linear S4N0 - Vs30, linear S1N0 - Tsite, linear S1N2 - Tsite, nonlinear (current NZS 1170 site-class model is basis of comparison) 5 0 Tsite Site-class Best fit minimises AIC = -2LL+2P -5 V s 30 LL = log-likelihood P = # of free coefficients (McVerry, PCEE) Period T(s) Nonlinear model required only at short periods T 0.3s Original site-class model best for spectral periods up to 0.2s Site-period (Tsite) model best for 0.3s and 0.5s period and longer V s 30 model poorer than Tsite model, much poorer for periods >0.75s

125 Amplification Site-response factors Tsite model and Class C & D models Site amplification wrt Class B rock for Tsite model Class D range solid Class C range dotted Tsite=0.1s Tsite=0.2s Tsite=0.3s Tsite=0.4s Class C resembles Tsite = 0.2s & 0.3s 2.50 Tsite=0.5s Tsite=0.6s D C Tsite=0.75s Tsite=1.0s Tsite=1.5s Tsite=2s Class D resembles Tsite = 1.5s curve Tsite=2.25s Spectral Period T(s) Shallow Soil Deep Soil Longer Tsite curves considerably exceed Class D curve (McVerry PCEE)

126 Spectral Shape Factor Proposed Changes to NZS 1170 Spectral Shape Factors NZS1170 Spectral Shape Factors and Proposed Tsite-dependent Curves (McVerry, PCEE) Dotted curves in shallow soil class Class C Shallow Soil Class D Deep or Soft Soil 2 Dashed curves in deep soil class Jump by factor of from Class C to D replaced by smooth transition with site period Tsite Class A/B Rock Tsite = 0.25s Tsite = 0.5s Tsite = 0.75s 1.5 Tsite = 1s Tsite = 1.25s Tsite = 1.5s 1 Tsite = 2s Class D 0.5 Class C Spectral Period T(s) Linear interpolation from Class C at Tsite = 0.25s to Class D at Tsite = 1.5s

127 Spectral Shape Factor Application Site Period Map (contour interval = 0.2s; red contour is 0.6s) 3.5 Spectral Shape Factors NZS1170 Spectral Shape Factors and Proposed Tsite-dependent Curves Dotted curves in shallow soil class Dashed curves in deep soil class Jump by factor of from Class C to D replaced by smooth transition with site period Tsite Class D Class C Class C Shallow Soil Class D Deep or Soft Soil Class A/B Rock Tsite = 0.25s Tsite = 0.5s Tsite = 0.75s Tsite = 1s Tsite = 1.25s Tsite = 1.5s Tsite = 2s Spectral Period T(s) (McVerry PCEE)

128 It s Our Fault ongoing & planned work Probabilistic liquefaction hazard assessment Simulation of ground motions resulting from rupture of the subduction interface under Wellington Comparison of ground motion modelling techniques at test sites in Wellington and Hutt Valley Earthquake loss modelling & recovery time estimation Review of earthquake planning & policy in Wellington region Vulnerability & welfare needs assessment

129 Some Christchurch EQ Lessons for NZ NZ Building Code We have much to be thankful for that NZ has a top-notch building code and that there is a high rate of compliance Earthquake Insurance EQC = very high percentage of private home owners have very good insurance cover for earthquakes Comparatively well integrated earthquake engineering & scientific communities GeoNet & NHRP Minimal duplication of effort (at least with regards to NZ researchers) A prioritisation of expertise focused on the issues that matter the most etc

130 Some Christchurch EQ Lessons for NZ Earthquake Prone Buildings are a big problem Imperative to increase the resilience of these buildings in Wellington (and elsewhere in NZ) Proactive stance of Wellington City Council on this issue is commendable and, based on the Christchurch experience, has been vindicated. And, in my opinion, performance goals should be further increased, and compliance timelines shortened Areas affected by permanent ground deformation, as well as shaking, suffer greater levels of damage and loss Liquefaction, Slope Failure, Surface Fault Rupture, Land-level changes Can render large areas unsustainable for post-earthquake habitation Liquefaction (including lateral spreading) Caused extensive damage to buildings and infrastructure in Christchurch The distribution of liquefiable sediments in the Wellington region is not as extensive as in Christchurch, but critical infrastructure and buildings in Wellington are located within these areas Catastrophic failure of the land (no matter what cause) when it leads to catastrophic failure of buildings & infrastructure needs to be proactively addressed Landuse performance criteria must be established and brought up to compatibility with building performance criteria

131 Some Christchurch EQ Lessons for NZ Landslides Hundreds of residences in Christchurch have been evacuated due to slope instability Wellington has more hilly country than Christchurch Compromised ability to fight post-earthquake fire (especially considering the extensive reticulated gas network in Wellington which is not the case in Christchurch) Post-earthquake fire In Wellington, must minimise number of ignitions, and maximise ability to fight fires at point of ignition Post-event functionality must be the goal (not just life safety) Long-term sustainability from earthquake attack is dependent on a number of factors: 1) the building, 2) infrastructure that services that building, 3) performance of neighbouring buildings, 4) wellbeing of the people in the community Need to fully integrate policies and legislation governing: 1) landuse planning, 2) building performance and 3) infrastructure performance Shelter in-place (dependent of limiting damage, not just achieving life-safety) Will increasingly influence ability to purchase insurance

132 It s Our Fault Publications Project Overview Van Dissen, R., Barnes, P., Beavan, J., Cousins, J., Dellow, G., Francois-Holden, C., Fry, B., Langridge, R., Litchfield, N., Little, T., McVerry, G., Ninis, D., Rhoades, D., Robinson, R., Saunders, W., Villamor, P., Wilson, K., Barker, P., Berryman, K., Benites, R., Brackley, H., Bradley, B., Carne, R., Cochran, U., Hemphill-Haley, M., King, A., Lamarche, G., Palmer, N., Perrin, N., Pondard, N., Rattenbury, M., Read, S., Semmens, S., Smith, E., Stephenson, W., Wallace, L., Webb, T., Zhao, J., 2010, It s Our Fault: better defining earthquake risk in Wellington. in proceedings, 11 th IAEG Congress, Auckland, New Zealand, 5-10 September, 2010: Van Dissen, R., Berryman, K., King, A., Webb, T., Brackley, H., Barnes, P., Beavan, J., Benites, R., Barker, P., Carne, R., Cochran, U., Dellow, G., Fry, B., Hemphill-Haley, M., Francois-Holden, C., Lamarche, G., Langridge, R., Litchfield, N., Little, T., McVerry, G., Ninis, D., Palmer, N., Perrin, N., Pondard, N., Semmens, S., Stephenson, W., Robinson, R., Villamor, P., Wallace, L., Wilson, K., 2009, It s Our Fault: Better Defining the Earthquake Risk in Wellington - Results to Date & a Look to the Future. in proceedings, New Zealand Society for Earthquake Engineering Technical Conference, Christchurch, New Zealand, 3-5 April, Paper No. 48, 8p. Likelihood Phase Wellington Fault Langridge, R., Van Dissen, R., Rhoades, D., Villamor, P., Little, T., Litchfield, N., Clark, K., Clark, D., 2011, Five thousand years of surface ruptures on the Wellington fault: implications for recurrence and fault segmentation. Bulletin of the Seismological Society of America 101 (5): doi: / Langridge, R.M., Van Dissen, R., Villamor, P., Little, T., 2009, It s Our Fault Wellington Fault paleoearthquake investigations: final report. GNS Science Consultancy Report 2008/344. Little, T.A., Van Dissen, R., Rieser, U., Smith, E.G.C., Langridge, R., 2010, Co-seismic strike-slip at a point during the last four earthquakes on the Wellington fault near Wellington, New Zealand. Journal of Geophysical Research 115. B doi: /2009jb Ninis, D., Little, T., Van Dissen, R., Smith, E., Langridge, R., 2010, The Wellington Fault - Holocene displacements and slip rates at Emerald Hill, Wellington, New Zealand: Progress Report. VUW Research Report No p. Rhoades, D.A., Van Dissen, R.J., Langridge, R.M., Little, T.A., Ninis, D., Smith, E.G.C., Robinson, R., 2011, Re-evaluation of conditional probability of rupture of the Wellington-Hutt Valley segment of the Wellington Fault. Bulletin of the New Zealand Society for Earthquake Engineering 44 (2): Rhoades, D.A., Van Dissen, R.J., Langridge, R.M., Little, T.A., Ninis, D., Smith, E.G.C., Robinson, R., 2010, It s Our Fault: Re-evaluation of Wellington Fault conditional probability of rupture. in proceedings, New Zealand Society for Earthquake Engineering Technical Conference, Wellington, New Zealand, March, Paper No. 23, 8p. Rhoades, D.A., Van Dissen, R.J., Langridge, R.M., Little, T.A., Ninis, D., Smith, E.G.C., Robinson, R., 2010, It s Our Fault Conditional probability of rupture of the Wellington-Hutt Valley segment of the Wellington Fault. GNS Science Consultancy Report 2010/16. 17p.

133 It s Our Fault Publications Wairarapa Fault Carne, R.C., Little, T.A., Rieser, U., 2011, Using displaced river terraces to determine Late Quaternary slip rate for the central Wairarapa Fault at Waiohine River, New Zealand. New Zealand Journal of Geology and Geophysics 54 (2): doi: / Little, T.A., Van Dissen, R., Schermer, E., Carne, R., 2009, Late Holocene surface ruptures on the southern Wairarapa fault, New Zealand: link between earthquakes and the raising of beach ridges on a rocky coast. Lithosphere 1 (1): doi: /l7.1. Schermer, E.R., Little, T.A., Rieser, U., 2009, Quaternary deformation along the Wharekauhau fault system, North Island, New Zealand: Implications for an unstable linkage between active strike-slip and thrust faults. Tectonics 28: TC6008, doi: /2008tc Villamor, P., Langridge, R.M., Ries, W., Carne, R., Wilson, K., Seebeck, H. & Cowan, L., 2008, It s Our Fault Wairarapa Fault slip rate investigations: completion report - Is the Wairarapa Fault slip rate decreasing to the north? GNS Science Consultancy Report 2008/170. Ohariu Fault Litchfield, N., Van Dissen, R., Hemphill-Haley, M., Townsend, D., Heron, D., 2010, Post c. 300 year rupture of the Ohariu Fault in Ohariu Valley, New Zealand. New Zealand Journal of Geology and Geophysics 53: doi: / Litchfield, N., Van Dissen, R., Hemphill-Haley, M., Townsend, D., Heron, D., 2010, It s Our Fault Ohariu Fault paleoearthquake investigations: final report. GNS Science Consultancy Report 2010/17: 31p. Cook Strait active faulting Barnes, P.M., Pondard, N., 2010, Derivation of direct on-fault submarine paleoearthquake records from high-resolution seismic reflection profiles: Wairau Fault, New Zealand. Geochemistry, Geophysics, Geosystems 11, Q doi: /2010gc Barnes, P.M., Pondard, N., Lamarche, G., Mountjoy, J., Van Dissen, R., Litchfield, N., 2008, It s Our Fault: active faults and earthquake sources in Cook Strait. NIWA Client Report WLG : 36 p. Pondard, N., Barnes, P.M., 2010, Structure and paleoearthquake records of active submarine faults, Cook Strait, New Zealand: Implications for fault interactions, stress loading, and seismic hazard. Journal of Geophysical Research 115, B doi: /2010jb Subduction zone earthquake geology & geodesy Beavan, J., Wallace, L., 2008, It s Our Fault Wellington geodetic and GPS studies: task completion report Fault coupling results from inversion of new and reprocessed GPS campaign data from the Wellington region. GNS Science Consultancy Report 2008/172. Clark, K., Hayward, B., Cochran, U., Grenfell, H., Hemphill-Haley, E., Mildenhall, D., Hemphill-Haley, M., Wallace, L., 2011, Investigating subduction earthquake geology along the southern Hikurangi margin using paleoenvironmental histories of intertidal inlets. New Zealand Journal of Geology and Geophysics 54 (3): Hayward, B., Grenfell, H.R., Sabaa, A., Kay, J., Clark, K., Ecological distribution of the foraminifera in a tidal lagoon-brackish lake, New Zealand, and its Holocene origins: Journal of Foraminiferal Research 41: Wallace, L.M., Barnes, P., Beavan, J., Van Dissen, R., Litchfield, N., Mountjoy, J., Lamarche, G., Pondard, N., accepted, The kinematics of a transition from subduction to strike-slip: an example from the central New Zealand plate boundary. Journal of Geophysical Research. Wilson, K., Cochran, U., 2008, It s Our Fault Past subduction zone ruptures: task progress report GNS Science Consultancy Report 2008/173.

134 It s Our Fault Publications Wellington region synthetic seismicity Robinson, R., Van Dissen, R., Litchfield, N., 2011, Using synthetic seismicity to evaluate seismic hazard in the Wellington region, New Zealand. Geophysical Journal International: doi: /j X x. Robinson, R., Van Dissen, R., Litchfield, N., 2009, It s Our Fault synthetic seismicity of the Wellington region: final report. GNS Science Consultancy Report 2009/192: 36 p. Effects Phase Wellington & Lower Hutt geological & geotechnical characterisation Boon, D.P., and others, in prep, Geological, geotechnical and subsoil class (NZS ) characterisation of Lower Hutt, New Zealand. To be submitted to New Zealand Journal of Geology and Geophysics. Boon, D., Perrin, N.D., Dellow, G.D., Van Dissen, R., Lukovic, B., 2011, NZS1170.5:2004 site subsoil classification of Lower Hutt. in proceedings, 9th Pacific Conference on Earthquake Engineering, Auckland, New Zealand, April, 2011: Paper 013, 8 p. Boon, D.P., Perrin, N., Dellow, G., Lukovic, B., 2010, It s Our Fault geological and geotechnical characterisation and site class revision of the Lower Hutt Valley. GNS Science Consultancy Report 2010/163. Fry, B., Stephenson, B., Benites, R., Barker, P., 2010, Seismic instrumentation and inversion for physical parameters of Wellington and the Hutt Valley. GNS Science Consultancy Report 2010/18: 43p. McVerry, G.H., Site-effect terms as continuous functions of site-period and Vs30. in proceedings, 9 th Pacific Conference on Earthquake Engineering, Auckland, New Zealand, April, 2011: Paper 010. Perrin, N.D., Stephenson, W.R., Semmens, S., 2010, Site class determinations (NZS ) in Wellington using borehole data and microtremor techniques. in proceedings, New Zealand Society for Earthquake Engineering Technical Conference, Wellington, New Zealand, March, Paper No. 22, 8p. Semmens, S., and others, in prep, Geological, geotechnical and subsoil class (NZS ) characterisation of central Wellington, New Zealand. To be submitted to New Zealand Journal of Geology and Geophysics. Semmens, S., Perrin, N.D., Dellow, G., Van Dissen, R., 2011, NZS :2004 site subsoil classification of Wellington City. in proceedings, 9th Pacific Conference on Earthquake Engineering, Auckland, New Zealand, April, 2011: Paper 007, 8 p. Semmens, S., Perrin, N., Barker, P., 2010, What lies beneath: Geological and geotechnical characterisation of the Wellington central commercial area. in proceedings, 11th IAEG Congress, Auckland, New Zealand, 5-10 September, 2010: Semmens, S., Perrin, N.D., Dellow, G., 2010, It s Our Fault geological and geotechnical characterisation of Wellington City. GNS Science Consultancy Report 2010/176: 48p. Subduction zone ground motion simulations Holden, C., Zhao, J., Modelling strong ground motions for subduction events in the Wellington region, New Zealand. in proceedings, 9th Pacific Conference on Earthquake Engineering, Auckland, New Zealand, April, 2011: Paper 229. Impacts Phase Social Science component Johnston, D.M., McClure, J., Becker, J.S., Paton, D., Finnis, K., Leonard, G.L., Wright, K., in review, Community understanding of earthquake and tsunami risk in Wellington, New Zealand. Cities at Risk: Living with Perils in the 21 st Century, Risk Perceptions and Behaviours: submitted.

135 Geoscience Society of New Zealand Hochstetter Lecture 2011 Presented by: Russ Van Dissen (on behalf of the It s Our Fault team)