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Project Number: 5-MB97C.02 Waitohi Picton Precinct Re-development

15 October 2020 CONFIDENTIAL

Slope, Seismic and Tsunami Hazards Assessment Contact Details

Bill Leask WSP L9 Majestic Centre 100 Willis Street 6011 +64 4 471 7000 +64 27 240 2274 [email protected]

Document Details: Date: 15 October 2020 Reference: GER 2020/16 Status: Issue 3

Prepared by

Bill Leask

Helen Hendrickson

Reviewed by

Campbell Keepa

Approved for release by

Matthew Taylor

©WSP Limited 2020 i Document History and Status Revision Date Author Reviewed by Approved by Status Issue 1 29 May W Leask C Keepa M Taylor 2020 H Hendrickson Issue 2 2 Sep 2020 W Leask C Keepa M Taylor H Hendrickson Issue 3 15 Oct 2020 W Leask C Keepa M Taylor H Hendrickson

Revision Details Revision Details Issue 2 Revised following reviews by Mitchell Daysh Issue 3 Revised following Phase 2 analysis

©WSP New Zealand Limited 2020 ii Contents

Disclaimers and Limitations ...... 1

1 Introduction ...... 2 1.1 Purpose and scope ...... 2 1.2 Referenced documents ...... 2

2 The Site ...... 2 2.1 Location ...... 2 2.2 Project area ...... 3

3 Geological Setting ...... 3 3.1 Geomorphology and stratigraphy ...... 3 3.2 Groundwater ...... 4 3.3 Faulting ...... 4

4 Slope Hazards ...... 6 4.1 Slopes adjacent to Port Marlborough ...... 6 4.2 Slope hazard ...... 6

5 Seismic Hazards...... 6 5.1 Previous earthquakes ...... 6 5.2 Surface rupture hazard ...... 8 5.3 Earthquake ground shaking hazard...... 8 5.4 Tectonic land movement ...... 12

6 Liquefaction Hazard ...... 12 6.1 Liquefaction in previous earthquakes ...... 12 6.2 Liquefaction and Soil Cyclic Softening ...... 12 6.3 Free Field Settlements ...... 14 6.4 Lateral Spreading Hazard ...... 14

7 Tsunami and Seiche Hazard ...... 16 7.1 Tsunami and Seiche ...... 16 7.2 Wave heights and inundation areas ...... 16 7.3 Tsunami sources and arrival times ...... 17

8 Summary of Natural Hazards ...... 18

9 Managing Risk from Natural Hazards ...... 19 9.1 Evaluating risk from natural hazards ...... 19 9.2 Climate change ...... 20

©WSP New Zealand Limited 2020 iii 9.3 Risk management options ...... 20

10 References ...... 20

List of Figures Figure 1: Location of Port Marlborough, Picton. Map extracted from https://www.topomap.co.nz, accessed 1 May 2020. Grid lines are spaced at 10 km...... 2 Figure 2. Aerial photograph map of Picton with the project area outlined in yellow (Source: https://maps.marlborough.govt.nz/) ...... 3 Figure 3. Geological map of the Picton area, extracted from the 1:250 000 QMAP Wellington (Begg & Johnston 2000). The Q1n area in pale yellow is the approximate area of reclamation...... 4 Figure 4. Active faults in the Marlborough – – Wellington region (from Wallace et al. 2012)...... 5 Figure 5: Kaikōura Earthquake Damage Observations ...... 8 Figure 6: Comparison of 5% damped response spectra from PSHA and NZS 1170.5...... 10 Figure 7: Amplification between effective bedrock at 90 m depth to the surface for 25, 50 and 2500 year return period events...... 11 Figure 8: Typical Stability Section (Behind Wharves)...... 15 Figure 9: Typical Stability Analysis (Carpark and Terminal Building) ...... 15 Figure 10: MDC Tsunami evacuation zones in Picton (from Heron et al. 2015)...... 17

List of Tables Table 1. Active Fault Summary (from Stirling et al. (2012) supplementary data)...... 5 Table 2 - Strong Motion Data Summary for the Picton Queen Charlotte College Station ...... 7 Table 3 - Design Peak Ground Accelerations...... 9 Table 4: Tabulated PSHA site specific uniform hazard spectra (Bradley 2020)...... 10 Table 5 - Characteristic Soil Profile for Site Response Analysis ...... 10 Table 6: Wave Return Periods and Heights in the Tasman Bay/Cape Jackson section (Power, 2014)...... 17 Table 7. Summary of natural hazards...... 18

©WSP New Zealand Limited 2020 iv Project Number: 5-MB97C.02 Waitohi Picton Ferry Precinct Re-development Natural Hazards Assessment

Disclaimers and Limitations This report Waitohi Picton Ferry Precinct Re-development – Slope, Seismic and Tsunami Hazards Assessment has been prepared by WSP exclusively for Port Marlborough New Zealand and KiwiRail Holdings Ltd in relation to and in accordance with the agreement with the client. The findings in this Report are based on and are subject to the assumptions specified in the contract and this report. WSP accepts no liability whatsoever for any reliance on or use of this Report, in whole or in part, for any use or purpose other than the Purpose or any use or reliance on the Report by any third party.

©WSP New Zealand Limited 2020 1 Project Number: 5-MB97C.02 Waitohi Picton Ferry Precinct Re-development Natural Hazards Assessment

1 Introduction

1.1 Purpose and scope

WSP has been commissioned by Port Marlborough New Zealand (PMNZ) and KiwiRail Holdings Ltd to provide concept design and engineering inputs for the proposed Waitohi Picton Ferry Precinct re-development.

The Waitohi Picton Ferry Precinct is a critical infrastructure component for connections between the North and South Islands. Damage and disruption to the port may cause direct and secondary economic losses to the port, its stakeholders and the wider region. This report presents an assessment of the seismic, tsunami and slope hazards that the port is exposed to within the project area, including the potential hazard effects and consequences to the port site.

Coastal hazards including the potential for scour and erosion or sedimentation and hydrological hazards including pluvial or fluvial flooding have been assessed separately and are outside the scope of this report. Volcanic hazards and wildfire are also excluded from this assessment.

1.2 Referenced documents This report should be read in conjunction with the following reports:

· WSP (2020a) Picton Ferry Precinct – Factual Geotechnical Report, Issue 2 including Priority A and B site investigations · WSP (2020b) Picton Ferry Precinct – Ground Conditions Assessment Report · Bradley Seismic (2020) Probabilistic seismic hazard analysis for Port Marlborough · WSP (2020c) Picton Ferry Precinct - Site Response Analysis Report 2 The Site

2.1 Location Port Marlborough is located immediately north of the Picton township, within Queen Charlotte Sound, and includes the terminal for the Cook Strait . The location of the port is shown in Figure 1.

Port Marlborough, Picton

Figure 1: Location of Port Marlborough, Picton. Map extracted from https://www.topomap.co.nz, accessed 1 May 2020. Grid lines are spaced at 10 km.

©WSP New Zealand Limited 2020 2 Project Number: 5-MB97C.02 Waitohi Picton Ferry Precinct Re-development Natural Hazards Assessment

2.2 Project area The area covered by this assessment includes the ferry terminals, rail marshalling yards and vehicle marshalling areas, and extends from the outer reaches of the harbour wharves to the north, Lagoon Road to the west, Auckland Street to the east and Broadway to the south (Figure 2).

Lagoon Rd

Auckland St Dublin St

Broadway

Figure 2. Aerial photograph map of Picton with the project area outlined in yellow (Source: https://maps.marlborough.govt.nz/) 3 Geological Setting

This section summarises the geomorphology, stratigraphy, groundwater conditions and faulting at the site. The geology and ground conditions at the site are covered in more detail in the Site Investigations Factual Report (WSP 2020a) and the Ground Conditions Report (WSP 2020b).

3.1 Geomorphology and stratigraphy Picton is situated in a drowned river valley, bounded by steep hillsides with a variety of bedrock types (Nicol & Campbell 1990; Begg & Johnston 2000) (Figure 3). The floor of the valley is filled with alluvial outwash deposits, overlain by estuarine and marine sediments. From the early to mid 1900’s, the original Waitohi River estuary was reclaimed in several stages to a level of 4 to 5 m above mean sea level.

Bedrock in the Ferry Precinct area is mapped as Arapawa Lithologic Association (Tp on Figure 3) that comprises predominantly indurated sandstone with no metamorphic textural overprint (Begg & Johnston 2000). Also seen at the port is Picton Conglomerate (Oligocene age), comprising slightly weathered, strong, calcite-cemented conglomerate of fine to coarse-grained gravel.

©WSP New Zealand Limited 2020 3 Project Number: 5-MB97C.02 Waitohi Picton Ferry Precinct Re-development Natural Hazards Assessment

Figure 3. Geological map of the Picton area, extracted from the 1:250 000 QMAP Wellington (Begg & Johnston 2000). The Q1n area in pale yellow is the approximate area of reclamation.

3.2 Groundwater Groundwater was encountered in the site-specific investigations between 1.5 m and 3.0 m depth, and is expected to be tidally-influenced near the edge of the reclamation. Groundwater may also be affected by groundwater flows from the surrounding hills and Waitohi River. Seep fields and plumes have been observed throughout Queen Charlotte Sound forming underwater craters as the pressure from the seeps disperses the soft mud seafloor. Basement rocks have numerous planes of weakness, giving them permeability, enabling water to rise to the surface. Artesian or sub-artesian pressures may be present at depth within the rock and alluvium but were not apparent in the borehole investigations.

3.3 Faulting The plate boundary between the Pacific and Australian plates passes through Marlborough as the , which links the transform plate boundary to the southwest to the westward-directed Hikurangi margin to the northeast. Consequently, this site is an area of moderate seismicity, as relative motion between the tectonic plates is accommodated with slip at the plate interface and on shallow crustal faults (Wallace et al., 2012).

Likely sources of strong ground shaking at Picton include the Hikurangi Subduction Interface, and faults within the Marlborough Fault System. It is possible that multiple rupture scenarios can occur in the same event along different faults, creating long duration strong ground motions such as those seen in the .

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Although many inactive faults are shown on the geological map of the Picton area (Figure 3), active faults in the wider region (Figure 4) are the primary contributors to the seismic hazard at the site. The major active crustal faults in this region are summarised in Table 1. The Hikurangi Interface fault is a complex active seismic source capable of producing Mw 9.0 earthquakes depending on the area of fault rupture.

PICTON

Leading edge of Hikurangi subduction interface

Figure 4. Active faults in the Marlborough – Cook Strait – Wellington region (from Wallace et al. 2012).

Table 1. Active Fault Summary (from Stirling et al. (2012) supplementary data).

Fault Characteristic Recurrence Distance Direction Event Interval from Magnitude (yrs) site (km) 7.0-7.7 1000 18 South 7.7 4210 36 South 7.7 1990 70 South (Conway) 7.1 220 115 South (Wn-Hutt) 7.5 840 55 East Alpine Fault (Kaniere-Tophouse) 7.7 620 100-280 South West 8.2 1200 86 East Jordan-Kekerengu-Needles 7.6 390 78 South

Notes: 1) Wairau Fault data from Nicol & Van Dissen (2018). 2) Vernon Fault considered as a splay of Awatere Fault.

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4 Slope Hazards

4.1 Slopes adjacent to Port Marlborough A steep-sided ridge with peaks of 155 m and 130 m above sea level runs immediately to the west of the port boundary. LiDAR, historical and present day aerial imagery have been assessed showing no evidence of deep-seated land sliding in the area around the port.

Slopes along Lagoon Road are locally very steep, and outcrops range from intact, tight rockmass to dilated, closely-fractured rock. Localised small rockfalls have been identified along the cut of Queen Charlotte Drive due to instability in the overlying surficial material. Small amounts of debris are confined to the road side ditch. Small and localised residual soil failures have also been identified in historical aerial imagery on bare grass slopes, but since 1990 this area has become vegetated in scrub, improving stability.

The slopes were observed to be generally stable with relatively minor slips observed in the overlying residual soils. PMNZ staff have not encountered slope failures around the port.

4.2 Slope hazard There is the possibility for slope failure events to occur, but under present day conditions the risk is low. Increased storm frequency and rainfall intensity from climate change may increase the risk of slope instability in time, but the effects of climate change are uncertain.

Strong earthquake shaking at the site could cause slope instability and dilate rock and soil increasing the vulnerability of slopes to further instability when groundwater pressures are elevated during storms or from seasonal fluctuations in the years following. 5 Seismic Hazards

5.1 Previous earthquakes

5.1.1 Historic Earthquakes There have been several previous earthquakes that have caused damage to buildings in the Picton township. These occurred in 1862, 1863 and 1959, with the latter being the most serious (Kelly, 1976). The sources of these earthquakes are not known, and the dates do not coincide with large earthquakes in other parts of the country.

In the Marlborough Earthquake of 1848, where a 105 km long section of the Awatere Fault ruptured ca. 33 km south of Picton, there are no reports of significant damage in Marlborough (possibly due to the small population at the time) but ground shaking was reported to be very strong causing collapse of chimneys and 3 fatalities in Wellington (McKinnon, 2016).

5.1.2 The 2013 Cook Strait and 2016 Kaikōura Earthquakes

5.1.2.1 Strong Ground Motion Records Strong ground motion records have been obtained from the NZ Strong Ground Motion database for the Kaikōura and Cook Strait earthquakes. Peak ground accelerations recorded at nearby strong motion monitoring stations are summarised in Table 2.

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Table 2 - Strong Motion Data Summary for the Picton Queen Charlotte College Station

Distance Peak Ground Earthquake Date and Time Magnitude Depth epicentre - Acceleration station 14/11/2016 Kaikōura 7.80 15.1 km 178 km 0.26 g 12.02 am Cook Strait 21/07/2013 6.54 16.8 km 44 km 0.16 g (Seddon) 5.09 pm Source: https://www.geonet.org.nz/data/supplementary/nzsmdb, accessed May 2020.

5.1.2.2 Kaikōura Earthquake Damage WSP Opus completed a post-earthquake inspection of Port Marlborough following the M 7.8 earthquake on 14 November 2016 (WSP Opus, 2016). In addition to this, a site walkover was completed on 8 July 2019 by WSP Opus Geotechnical Engineers and a Ports Engineer from Port Marlborough as part of the current project.

Structural and geotechnical earthquake damage was observed at several locations around the port. A summary of the ground related earthquake damage observed and reported included:

1 Dislodging of mortar pile caps at No. 2 Short-Arm Wharf. 2 Buckling of steel plates due to relative movement between land and wharf at the landward end of No. 2 Short-Arm Wharf. 3 Cracking in pile heads along western side of wharf adjacent to electrical substation. Gaps were evident between piles and embankment slope due to kinematic movement of the ground at No. 2 Short-Arm Wharf. 4 Lateral spreading around the electrical substation at No. 2 Short-Arm Wharf. 5 Shear failure of sheet pile wall capping beam and lateral spreading leading to pavement cracking of up to 20 mm and settlement of the ground of up to 100 mm at the Lady Bridget Linkspan. 6 Settlement and horizontal displacement (less than 10 mm) at the southern end of the Waimahara Wharf. Settlement of rip rap underneath and immediately downslope of retaining wall. 7 Horizontal movement and subsidence of the revetment slope beneath the Picton ferry terminal building leading to differential settlement of foundations between the reclamation and seaward piled section of the building, tilting of the piles towards the sea and a 20 mm gap opening between the building foundation and adjacent wharf. Cracking in foundation walls due to settlement and displacement of a floor slab at a construction joint.

The locations of the ground movement related earthquake damage reported in WSP Opus (2016) and observed in the site walkover are shown in Figure 5.

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Differential Lateral Spreading at settlement of No. 2 Short Arm (5) terminal building foundations. Rotation of piles under terminal building

Gap between jetty and wall (7)

Row of buildings which tilted towards the sea (7)

Figure 5: Kaikōura Earthquake Damage Observations

5.2 Surface fault rupture hazard Infrastructure-crossing active faults can be severely damaged by the metres of horizontal and vertical fault displacement and the associated shear deformation of the soils overlying the fault that can occur when the fault ruptures.

As the faults mapped in the Picton area (Figure 3) are considered inactive, the risk of surface fault rupture causing damage and disruption to the ferry terminal is considered low.

5.3 Earthquake ground shaking hazard

5.3.1 Probabilistic Seismic Hazard Analysis A site specific probabilistic seismic hazard analysis (PSHA) has been completed by Bradley Seismic Ltd (Bradley, 2020) and should be referred to for a more detailed summary of the seismic hazard at this site. The probabilistic study was conducted in OpenSHA using the latest national consensus earthquake rupture forecast reported in Stirling et al. (2012), and a total of 8 different ground motion models were weighted within a logic tree approach to assess uncertainty. These are different to the earthquake rupture forecast and ground motion models used to develop the loadings code NZS 1170.5: 2004.

The ground conditions change earthquake waves as they travel from rock to the surface. The average shear-wave velocity over the top 30 m of the ground profile (Vs30) is used to characterise ground conditions in the ground motion models. A Vs30 of 205 m/s has been selected for the PSHA based on shear-wave velocity measurements where critical infrastructure will be built for the PFPD and corresponds to a deep soil site (Class D) in NZS 1170.5. The thickness and stiffness of the soils vary across the site, and ground motion characteristics near the foot of the hills may be different to those in the PSHA.

Disaggregation of the probabilistic hazard analysis shows that in all cases, the seismic hazard at the site is dominated by known active faults in the region (Table 1, Figure 4). The most significant active faults contributing to the hazard at the port are the Wairau, Wairarapa, Jordan-Kekerengu-

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Needles faults and the Hikurangi subduction interface. The percentage contribution of each fault varies by return period and structural period. Further details are in the report by Bradley (2020).

Peak ground acceleration is a measure of earthquake intensity commonly used to characterize earthquake ground shaking in geotechnical earthquake engineering. Generally, the higher the peak ground acceleration, the greater the ground damage. The duration of shaking which is related to the magnitude of the earthquake and the frequency content of shaking, commonly defined by response spectra in seismic engineering also affect how damaging an earthquake is to the built environment.

The design peak ground accelerations and mean magnitudes recommended for design, adopted from the PSHA, are presented in Table 3.

Table 3 - Design Peak Ground Accelerations.

PSHA recommended Values Design Mean Peak Ground Earthquake Return Period Magnitude Acceleration (T = 0 s) (g) 25 6.43 0.11 100 6.77 0.20 500 6.99 0.34 1000 7.04 0.41 2500 7.08 0.51

Uniform hazard structural response spectra calculated from the PSHA, Class D spectra for the site calculated from 1170.5 (5% damped) and 80% of class D NZS 1170.5 spectra for return periods of 100, 1000 and 2500 years are shown in Figure 6. The site specific uniform hazard spectra (from the PSHA, Bradley 2020) for five return periods are tabulated in Table 4.

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Figure 6: Comparison of 5% damped response spectra from PSHA and NZS 1170.5.

Table 4: Tabulated PSHA site specific uniform hazard spectra (Bradley 2020).

Return Period (years) Period, 25 100 500 1000 2500 T (s) 0.0 0.111 0.202 0.340 0.409 0.510 0.1 0.210 0.381 0.639 0.773 0.974 0.2 0.279 0.512 0.867 1.049 1.324 0.3 0.272 0.505 0.857 1.034 1.293 0.4 0.240 0.458 0.795 0.964 1.207 0.5 0.213 0.417 0.750 0.915 1.154 1.0 0.125 0.275 0.582 0.759 1.020 1.5 0.077 0.184 0.412 0.550 0.768 2.0 0.052 0.134 0.314 0.422 0.594 3.0 0.029 0.080 0.183 0.246 0.347 4.0 0.020 0.056 0.128 0.171 0.242 5.0 0.015 0.043 0.097 0.130 0.185

Spectra calculated from the PSHA are similar to those in NZS 1170.5 at low return periods (e.g. 100 years) but are lower for periods up to 1 s for higher return periods (1000 years and greater). For seismic design of new infrastructure for the PFPD, we recommend the greater of spectral ordinates from the PSHA or 80% of the NZS 1170.5 spectra.

5.3.2 1D Site Response Analysis A site response analysis has been completed and is presented in WSP (2020c).

Site response analysis is a dynamic tool that models seismic wave propagation through soil. Site response analysis is used to determine the influence of non-linear soil stress-strain soil response and soil damping. These factors can significantly affect the strong ground motion response and seismic behaviour observed at a given site.

The analysis was completed using selected ground motions provided by Bradley (2020).

The ground profile was developed using interpreted soil parameters from the priority A and priority B active and passive surveys, cone penetrometer test results, borehole logs and laboratory testing. Degradation curves were modelled using Darendeli (2001).

A total stress 1-D non-linear analysis was carried out based on the soil profile summarised in Table 5.

Table 5 - Characteristic Soil Profile for Site Response Analysis

Depth (m Soil Unit bgl) 0 – 3 Reclamation fill 3 - 8 Marine 1 8 - 13 Marine 2 13 – 90 Alluvium with increasing stiffness

Ten effective-bedrock earthquake records were selected and scaled to 80% of NZS1170.5 site class A (rock site) for a 500-year return period. Within profile motions were obtained by deconvoluting the surface motions to 90 m depth through rock using the software package Deepsoil®. The

©WSP New Zealand Limited 2020 10 Project Number: 5-MB97C.02 Waitohi Picton Ferry Precinct Re-development Natural Hazards Assessment within motions were then applied to the site soil profile using a rigid base. Scaling factors provided in Bradley (2020) were applied to these motions to obtain motions applicable to other return periods.

The analysis showed significant motion amplification of waves with periods around 1 second. Amplification primarily occurred through the marine silts. It is expected that this will have the biggest impact on the seawalls, terminal building and jetties.

Figure 7 summarises the amplifications from 90 m to the surface for three return periods. Note that for the 500 and 2500-year return period earthquakes, maximum shear strains of 1% and 5% respectively were output in the marine layers. 1% shear strain is considered the limit to which current methods can accurately represent soil response.

5 4.5 4 3.5 3 2.5 1D Deepsoil (RP 50) 2 1D Deepsoil (RP 500) 1.5 1D Deepsoil (RP 2500) 1

Amplification -Amplification / RS(90m) RS(0m) 0.5 0 0.01 0.1 1 10 Period (s)

Figure 7: Amplification between effective bedrock at 90 m depth to the surface for 25, 50 and 2500 year return period events.

5.3.3 Basin Effects Basin edge effects can have a strong influence on ground motions. Basins tend to trap seismic waves resulting in elongation of the shaking duration and an increase in the amplitude of shaking. When waves exiting the basin hit the bedrock boundary, some of the waves are reflected back while some of the waves pass through the boundary, refracting as they do so. This occurs because of the high stiffness contrast between the bedrock and the overlying sediments, and because of the inclined angle of the bedrock. Consequently, earthquakes within basins tend to be longer (because waves become trapped) and have higher intensity shaking (because of the superposition of these trapped waves).

Another consequence of basin geometry is the basin edge effect. The basin edge effect is caused by the constructive interference between surface waves and body waves. This constructive interference causes large accelerations at the surface near the edge of the basin. In past events across the world, basin edge effects have increased spectral response at periods > 0.5 s. One final consequence of the basin geometry is the potential for focussing. Due to the spherical nature of basins, there is likely to be localised areas where body waves are refracted together, and the ground shaking is of higher intensity.

The Picton harbour is within the head of a deep northeastwards-draining valley modified by sea- level fluctuation and regional tectonic subsidence. The valley is north-south orientated and is open to the north. It is possible that basin effects may occur with seismic waves becoming trapped in the valley and reflecting off the sides.

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5.4 Tectonic land movement The elevation of the New Zealand landmass is affected by both long-term tectonic movement, and by rapid displacement on faults associated with earthquakes.

Long-term vertical tectonic movement (over 1000’s of years) of the is estimated to be between 0 mm and -1 mm per year (Beavan & Litchfield, 2012). Inter-seismic land movement rates may be greater and could be either uplift or subsidence.

Fault movement can cause metres of either subsidence or uplift of land over wide areas to occur within seconds. These coseismic displacements can be in the order of tens of centimetres to several metres and are generally largest nearest the fault or faults that rupture, but can affect areas within tens of kilometres of the site. The consequences could be severe – increased vulnerability to any ensuing tsunami, coastal hazards, pluvial and fluvial flooding, effects on navigation and berthing etc.

Examples of coseismic displacements include the effects of the 2016 Kaikōura earthquake in Picton (Section 5.1.2.2 above), and uplift and subsidence caused by the 1855 Wairarapa Earthquake (Grapes & Downes 1997). Holocene coastal deformation on the was summarised by Clark et al. (2019), who attempted to distinguish subduction interface earthquakes from shallow-crustal earthquakes. Rupture on the Hikurangi subduction zone (approximately 45 km beneath Picton (Clark et al. 2019)) is possibly the biggest threat to the Picton area, but we are not aware of any research on the likely coseismic subsidence/uplift at Picton from this source. There are no conventional methods to assess the likely coseismic displacement at a site, and therefore a research level study would be required. 6 Liquefaction Hazard

6.1 Liquefaction in previous earthquakes There were no surface ejecta observed at the port in either the Cook Strait or Kaikōura earthquakes that would confirm liquefaction developed in these events. However, limited liquefaction may have developed at depth and may have contributed to the lateral movement and subsidence observed near the margins of the reclamation.

6.2 Liquefaction and Soil Cyclic Softening Soils susceptible to liquefaction are traditionally thought of as loose to medium dense, saturated sands and low plasticity silts. Liquefaction of gravelly soils has also been observed at CentrePort in Wellington, the port of Kobe, Japan, and ports in and Alaska.

The effects of soil liquefaction may include ground subsidence, soil and water ejecta at the surface, lateral spreading of revetment slopes, increased pressures on seawalls, reduced foundation support for structures, increased loads imposed on piles from ground movement and high buoyancy forces on buried structures. Consequently, liquefaction can cause severe damage to structures, underground services, rail and pavements.

Susceptibility of the site soils to liquefaction, the return period of shaking where liquefaction is triggered and the effects of liquefaction have been evaluated using conventional simplified methods described in the New Zealand Geotechnical Earthquake Engineering Guidelines, Module 3. In previous borehole site investigations at Picton that included SPTs, the SPT hammer energy and sampler type have not been recorded and there is generally a lack of information to assess fines content. Therefore, most of the previous site investigations at Picton are not suitable for liquefaction hazard evaluation.

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This liquefaction assessment has been completed using all of the priority A and B site investigation data and laboratory testing to date. Cyclic triaxial testing is currently underway on the silt portion of the marine deposits (clay-type behaviour) to evaluate the potential for cyclic softening.

6.2.1 Reclamation Fill Susceptibility Site investigations show the reclamation fill to be in two layers, an upper layer of compacted gravels and a lower layer of looser gravels.

Gravelly soils below the water table are typically susceptible to liquefaction where the gravel particles are supported in a matrix of low plasticity sands and silt and the sand / silt properties govern the cyclic response (Cubrinovski 2019). This typically occurs when the gravelly soils contain more than about 30% sand and silt by weight, i.e. less than 70% of the soil is gravel.

Particle size analysis of the reclamation fill shows the gravel content to range between 55% and 78%. The lower reclamation fill typically has a higher sand and fines content and the matrix has low or no plasticity. The behaviour of the matrix is expected to be dominated by the sand portion as it is relatively large in comparison to the fines portion. This suggests that at least some parts of the reclamation fill may be susceptible to liquefaction.

6.2.2 Marine Deposits Susceptibility The marine sediments comprise loose to medium dense sands and silt of varying plasticity. Site investigations suggest that the marine deposits are generally in two layers, an upper layer of interbedded silty sands and silts, and a lower layer of silts with clay type behaviour (PI > 7 and Ic = 2.6 to 3.2) which extends down to the gravel alluvial deposits. The upper sands and the low plasticity or non-plastic silts are susceptible to liquefaction.

6.2.3 Triggering Simplified empirical liquefaction triggering analysis (Boulanger & Idriss, 2014) using CPT data indicates that liquefaction is triggered at a PGA of 0.12 g to 0.17 g (for a magnitude 6.4 earthquake). The triggering level of shaking is approximately equivalent to a 50 year return period earthquake. Potentially liquefiable layers are predominantly < 2.5 m thick above 6 – 12 m depth with layers up to 4.0 m thick being encountered in CPT026 and sCPT05. The liquefiable layers are most extensive in the area of the existing terminal carpark and parts of the existing marshalling yard.

The majority of marine soils below 6 – 12 m depth are too plastic to liquefy. The potential for cyclic softening to occur has been determined based on the method presented in Boulanger & Idriss (2007) implemented using the software package CLiq®. Cyclic softening was identified consistently across the site in the marine silts and was found to trigger at 1 in 100 year return period events and above.

The factor of safety against cyclic failure is just an indicator of the potential for softening, it does not provide an estimation of the soil strength losses and potential deformation. In the absence of site specific testing, a strength loss of 20 % has been assumed for the softened layers in accordance with WSDOT (2006).

The alluvium comprises layers of medium dense to very dense gravels with varying portions of sand, silt and clay and layers of stiff to hard plastic silts with occasional, typically thin layers of medium dense sand and silty sand. This unit typically appears to have a low potential for liquefaction, although in strong earthquakes, limited liquefaction is expected below 11 m depth in sand layers which are < 0.5 m thick and lensoidal.

The performance observed in the Kaikōura earthquake is not consistent with the levels of liquefaction predicted by simplified empirical methods. Potential reasons why performance in the Kaikōura earthquake does not match the predicted liquefaction response include:

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· The level of shaking experienced at the port in the Kaikōura Earthquake may be lower than the level of shaking measured at the nearest strong motion station at Queen Charlotte College (1.6 - 1.7 km from the ferry terminal). · The liquefaction resistance of the soils is under-estimated by conventional empirical methods. · Site system effects or the limited lateral extents of liquefiable layers reduces the damage caused by liquefaction.

The potential for liquefaction and lateral spreading will have significant impacts on the seismic performance and concept designs for seawalls, linkspans, jetties and foundations for the terminal building. Given the discrepancy between the observed liquefaction and the predicted liquefaction and liquefaction effects, it could be beneficial to undertake cyclic testing as it may allow for a more economic design.

During the priority B investigations, push tube sampling was undertaken with the intention of collecting samples suitable for cyclic liquefaction testing. Unfortunately, the sampling was not successful due to the loose and saturated nature of the soils.

Sampling using Dames & Moore samplers was undertaken to collect samples suitable for cyclic triaxial testing. Unfortunately the upper marine sands were not encountered at the test location as originally expected. Dames & Moore sampling of the marine silts was successful and cyclic triaxial testing is currently underway to confirm the potential for cyclic softening.

6.3 Free Field Settlements Free field settlements are the settlement the ground will undergo regardless of crust thickness or any structures being present. They are settlements related to consolidation of liquefied deposits only, and do not take into account other mechanisms of post-liquefaction settlement such as ejection of liquefied soils to the surface or shear induced settlements caused by lateral spreading of the reclamation Subsidence of structures with shallow foundation systems on liquefiable ground may be greater than free field subsidence, but structures supported on piles founded below liquefiable soils will generally experience much less subsidence.

Free field settlements from reconsolidation of liquefied soils have been estimated using the method by Zhang et al. (2002) implemented in CLiq®. Free field settlements in the range of 40 – 190 mm are predicted for a 1 in 100 year return period event. The estimates of free field subsidence suggest a low to moderate liquefaction hazard. The liquefaction hazard is greatest in the northern reclaimed areas where the potentially liquefiable reclamation fill and marine deposits are thickest.

Total subsidence in an earthquake could be greater due to tectonic movement, lateral spreading and ejection of liquefied soils to the surface. Settlement of structures will be influenced by their foundation type and soil-structure interaction effects and is considered for individual structures in the design.

6.4 Lateral Spreading Hazard

6.4.1 Post-Earthquake Stability Large horizontal and vertical movement of the seawall and revetment slope are possible when the soils in or below the slope liquefy. The post-earthquake stability of the revetment slope seawall has been assessed using limit-equilibrium slope stability analysis with post-earthquake soil strengths for all soils susceptible to liquefaction or cyclic softening and no ground acceleration. Where factors of safety are less than 1.1, horizontal and vertical ground movements can be substantial.

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Jetty, linkspan and back-up berth abutments

Post-earthquake stability has been assessed assuming that the land behind the slope is filled to a level of 4 m, rock revetment thickness of 3.5 m and a slope angle of 1.75 H:1 V with a level at the top of the armourstone of -9.25 m NZVD in the berth pocket. A typical section for the analysis is shown in Figure 8.

Figure 8: Typical Stability Section (Behind Wharves).

Terminal Building and Carpark Area

A surrounding ground level of RL 2.0 m, rock revetment thickness of 1.5 m and angle of 1.75:1 with dredging carried out to NZVD level -9.25 m for the ferries have been assumed in the analysis of the slope adjacent to the terminal building and car park area. A typical section for the analysis is shown in Figure 9.

Figure 9: Typical Stability Analysis (Carpark and Terminal Building)

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Assessment

The analysis for both locations (wharf abutments and carpark/terminal building) indicates a global static factor of safety of 1 or less with liquefied strengths applied to all layers for a distance of up to 12 m back from the crest of the reclamation. This confirms that significant instability and lateral spreading could be expected in the margins of the reclamation if all potentially liquefiable layers liquefy.

Based on the method presented in Tokimatsu & Osaka (1998), in a 1 in 100 year return period event, 190 – 1300 mm of permanent displacement can be expected at a distance 10 m back from the edge of the reclamation, while permanent lateral displacement of 200 – 1400 mm could be expected in a 500 year return period earthquake.

The impacts of lateral spreading on each individual structure will need to be considered in design. 7 Tsunami and Seiche Hazard

7.1 Tsunami and Seiche Tsunami have been historically recorded in the at Picton, Wairau River and The Grove (Turnbull & Hughes, 2017). Tsunami waves can be triggered by local, regional or distant earthquakes, volcanic eruptions, landslides, bolide impact or combinations of these events. The waves can travel quickly across open water but slow and increase in height as they approach the coast.

A seiche is a standing wave set up in a partially or fully enclosed body of water. It can lead to repetitive waves of large height with relatively long intervals between wave arrivals.

Effects of tsunami include:

· Inundation and flooding of low lying areas. · Large hydro-static and hydro-dynamic loads on structures causing uplift of wharf decks, increased lateral loads on piles, seawalls and bulkheads, displacement and damage to buildings and other infrastructure. · Debris impact and damming forces where debris collides with and then accumulates in front of a structure. Turnbull & Hughes (2017) identified several sources of such debris including the logs stored at Shakespeare Bay. Ship collisions can impart very large impulse loads on structures. · Scour of soils as the tsunami comes and flows seaward again, and from strong tsunami related currents in the hours and days after undermining foundations, seawalls and eroding the shoreline. · Sedimentation affecting navigation. · Development of seiche. · Strong currents in the hours and days after a tsunami, making harbour navigation difficult and sometimes unviable due to elevated velocities.

7.2 Wave heights and inundation areas Wave heights at the coast (relative to tide level) for different return periods have been calculated for 268 sections, each about 20 km long, around the North and South Islands, in a probabilistic tsunami hazard assessment for New Zealand (Power, 2014). Calculated maximum wave heights for the Tasman Bay / Cape Jackson section are summarised in Table 6. There can be significant variation in wave heights within a section and local topographical features may focus tsunami and increase the run-up height at the port. The tsunami hazard in Marlborough has been assessed in more detail for the purpose of establishing tsunami evacuation zones. However, details on wave heights are not provided in this study.

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Table 6: Wave Return Periods and Heights in the Tasman Bay/Cape Jackson section (Power, 2014).

50th percentile maximum 84th percentile maximum Return Period (yrs) wave height (m) wave height (m) 100 2.2 2.6 500 4.4 5.5 2500 7.6 9.7

Tsunami evacuation zones have been defined by Marlborough District Council (MDC), based on a study by Heron et al. (2015) to determine areas likely to be inundated by tsunami with different return periods (Figure 10). The yellow and orange areas encompass the area expected to be inundated by a 2,500 year tsunami (at 84% confidence). The orange area is approximately the area expected to be inundated by a tsunami with a 500 year return period. Co-seismic land subsidence could increase the areas of inundation.

Figure 10: MDC Tsunami evacuation zones in Picton (from Heron et al. 2015).

7.3 Tsunami sources and arrival times The most likely source of damaging tsunami in the Marlborough Sounds is tsunami caused by earthquakes rather than landslides and volcanic eruptions (Heron et al., 2015). Disaggregation of a probabilistic tsunami hazard assessment (Power, 2014) shows that rupture of local faults including the are the most likely sources of large tsunami with local sources contributing about 70% to the 2,500 year return period hazard. Regional and distant earthquakes are the more likely sources of moderate tsunami at Port Marlborough, contributing about 60% to the 500 year return period hazard.

Turnbull & Hughes (2017) identified wave arrival times from earthquakes at distant (e.g Peru and Chile), regional (e.g ) and local sources (faults in Cook Strait, Marlborough Sounds, eastern and Hikurangi Subduction Zone) as:

· > 3 hours for distant sources; · 1 to 3 hours for regional sources; · < 60 minutes for local sources, with most sources being less than 30 minutes.

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8 Summary of Natural Hazards

A summary of the hazard exposure, hazard effects and mitigation potential for the Port of Marlborough site is presented in Table 7 below.

Table 7. Summary of natural hazards.

MITIGATION PICTON EXPOSURE HAZARD EFFECT POTENTIAL HAZARD

No known active faulting N.A, hazard is low through the PFPD. Fault rupture

Assess risk and consider Long-term movement of Could affect drainage, in design of infrastructure 0 mm to -1 mm per year. navigation and levels. Design the Inter-seismic rate and the vulnerability to tsunami, reclamation and potential for co-seismic climate change, coastal infrastructure so that Tectonic movement have not been hazards, pluvial and movement heights can be adjusted if assessed. fluvial flooding required.

Design infrastructure to mitigate risk of damage Moderate to high seismic and outage in ground shaking hazard. Damage to surface and earthquakes that cause PGA = 0.34 g & 0.51 g for buried infrastructure, strong shaking and 500 y and 2500 y return movement of slopes. considering aftershocks. periods respectively, Mw = Disruption to operations. Response planning and 7 built in operational redundancy to reduce

Seismic Ground shaking Ground Seismic outage.

Moderate to high Ground improvement to potential for liquefaction Damage to the seawall, reduce the potential for and lateral spreading jetties, linkspans liquefaction and lateral near the seaward margins including the approach spreading. Design of of the reclamation. Low bridge, terminal building infrastructure to tolerate to moderate liquefaction foundations, pavements effects (reduce damage) potential in the and buried infrastructure. or to allow for quick lateral spreading lateral Liquefaction and Liquefaction marshalling yards and at Disruption to operations. repair to reduce outage Dublin Street.

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MITIGATION PICTON EXPOSURE HAZARD EFFECT POTENTIAL HAZARD

Increase the height of the reclamation and infrastructure to reduce the potential for Wave heights of 4.4 -5.5 inundation, tsunami m and 7.6 m to 9.7 m at warning system, safe the entrance to the Damage to jetties and evacuation areas sounds in a 500 y and linkspan, altered identified, and evacuation 2500 y return period bathymetry, scour, debris. procedures developed for tsunami respectively. Damage to landward ships and people on land. Inundation in a 500 y and structures in an Design of infrastructure higher return period inundating tsunami. for wave and debris loads tsunami. The potential for Tsunami & seiche Tsunami Changes to currents considering these could inundation will increase if occur shortly after strong there is co-seismic ground shaking, subsidence of the site. liquefaction and lateral spreading when tsunami is triggered by a local seismic source

9 Managing Risk from Natural Hazards

9.1 Evaluating risk from natural hazards

In evaluating the risk posed by each hazard and the wider implications for the resilience of the port, the following considerations should be taken into account:

· The frequency of each hazard and the time-varying magnitude of impacts; · that in the event of a large earthquake, numerous hazards will occur in unison and their compound effects should be considered; and that · An initial hazard event may trigger secondary effects, either in the short or long term. For example, aftershocks or landslides in the wet seasons following earthquakes that weaken slopes. To inform long term planning for the resilience of the port, these considerations should be incorporated into a comprehensive risk assessment. The assessment should evaluate potential combinations of hazard scenarios and account for the interrelation of hazards which can potentially compound impacts.

Defining the hazard risk, the acceptable level of outage and the level of service that is required following a natural hazard event will inform design and the development of risk management priorities. Where hazards cannot be fully mitigated or are determined to be outside the design life of port assets, emphasis should be put into the consideration of emergency planning and post- disaster preparedness.

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9.2 Climate change The role of climate change and sea level rise is particularly important to ensure new development considers long term effects. The increased storminess with climate change may change the slope hazard. Sea level rise may increase the tsunami and liquefaction hazards.

9.3 Risk management options Improving resilience and reducing risks to Port Marlborough and its stakeholders can be achieved using the following principles:

1 Improving the robustness of physical infrastructure to limit damage, disruption and repair costs following natural hazards. 2 Adapting systems operations to make them less vulnerable to outage. 3 Building in redundancy or adaptive capacity so that there is flexibility to adapt operations to meet potentially different needs or take advantage of new opportunities. For example, having a highly resilient back-up berth for RORO and passengers. 4 Being prepared. Having systems and facilities in place to respond quickly to an event will minimise disruption. This could include installation of seismic and displacement monitoring so that rapid assessment of damage and availability can be made after an event, having service agreements with contractors and stakeholders for emergency response and suitable financial facilities to instigate repairs quickly.

Some of these aspects have been addressed in a separate High Impact – Low Probability resilience study, which has been undertaken to inform design requirements for key assets across the precinct.

10 References

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