Active fault hazards in the Taupō District NJ Litchfield R Morgenstern P Villamor RJ Van Dissen DB Townsend SD Kelly GNS Science Consultancy Report 2020/31 August 2020 DISCLAIMER This report has been prepared by the Institute of Geological and Nuclear Sciences Limited (GNS Science) exclusively for and under contract to Taupō District Council. Unless otherwise agreed in writing by GNS Science, GNS Science accepts no responsibility for any use of or reliance on any contents of this report by any person other than Taupō District Council and shall not be liable to any person other than Taupō District Council, on any ground, for any loss, damage or expense arising from such use or reliance. Use of Data: Date that GNS Science can use associated data: May 2020 BIBLIOGRAPHIC REFERENCE Litchfield NJ, Morgenstern R, Villamor P, Van Dissen RJ, Townsend DB, Kelly SD. 2020. Active faults in the Taupō District. Lower Hutt (NZ): GNS Science. 114 p. Consultancy Report 2020/31. Project Number 900W2041-00 Confidential 2020 CONTENTS EXECUTIVE SUMMARY ....................................................................................................... V 1.0 INTRODUCTION ........................................................................................................1 1.1 Background and Context (from the Project Brief) ............................................. 1 1.2 Scope, Objectives and Deliverables ................................................................ 1 1.3 Fault Avoidance Zones and Fault Awareness Areas for District Plan Purposes 4 1.3.1 Fault Avoidance Zones .......................................................................................4 1.3.2 Fault Awareness Areas ......................................................................................5 1.4 Report Contents and Layout ............................................................................ 5 2.0 TAUPŌ DISTRICT ACTIVE FAULTS – EXISTING INFORMATION ........................... 6 2.1 Tectonic Setting ...............................................................................................6 2.2 Historical Seismicity .........................................................................................8 2.3 Previous Active Fault Mapping ...................................................................... 10 2.4 Paleoseismic Data ......................................................................................... 10 2.4.1 Lilburn Trench.................................................................................................. 13 2.4.2 Waihi and Poutu Fault Zones Natural Exposure Transects ............................ 14 3.0 FAULT AVOIDANCE ZONES ................................................................................... 17 3.1 Fault Mapping Methodology........................................................................... 17 3.2 Fault Attributes .............................................................................................. 19 3.3 Fault Avoidance Zone Construction Methodology .......................................... 20 3.4 Fault Avoidance Zones in the Tongariro Domain ........................................... 25 3.5 Fault Avoidance Zones in the Southern Taupō Domain ................................. 27 4.0 FAULT AWARENESS AREAS ................................................................................. 31 4.1 Fault Mapping Methodology and Attributes .................................................... 31 4.2 Fault Awareness Areas Construction Methodology ........................................ 32 4.3 Fault Awareness Areas in the Tongariro Domain ........................................... 35 4.4 Fault Awareness Areas in the Northern Taupō and Whakamaru Domains ..... 37 4.5 Fault Awareness Areas in the Eastern Taupō District .................................... 39 5.0 ADVICE ON ACTIVE FAULT HAZARDS AND INCORPORATION INTO THE DISTRICT PLAN ....................................................................................................... 41 5.1 Recurrence Intervals...................................................................................... 41 5.1.1 Existing Data ................................................................................................... 41 5.1.2 Recurrence Interval Classes ........................................................................... 45 5.2 Recommendations for Incorporation for Planning Purposes .......................... 46 5.2.1 Guiding Principles ........................................................................................... 46 5.2.2 District Plan Maps ........................................................................................... 48 5.2.3 Fault Avoidance Zones .................................................................................... 48 5.2.4 Fault Awareness Areas ................................................................................... 51 5.2.5 Land Information Memoranda and Property Information Memoranda ............ 52 5.3 Ground-Surface Rupture Hazard ................................................................... 52 5.3.1 Ground-Surface Rupture Features .................................................................. 52 GNS Science Consultancy Report 2020/31 i Confidential 2020 5.3.2 Ground-Surface Rupture Impacts on Small to Medium Timber-Framed Houses ........................................................................................................................ 54 5.4 Active Fault Completeness ............................................................................ 55 5.5 Recommendations for Work Needing to be Undertaken for an Individual Wishing to Build in a Fault Avoidance Zone or Fault Awareness Area ........... 57 6.0 RECOMMENDATIONS ............................................................................................. 59 7.0 ACKNOWLEDGEMENTS ......................................................................................... 60 8.0 REFERENCES ......................................................................................................... 60 FIGURES Figure 1.1 Active faults in the high-resolution version of the New Zealand Active Faults Database .............. 3 Figure 2.1 Tectonic setting of the Taupō District ........................................................................................... 7 Figure 2.2 Epicentres of shallow (≤40 km) earthquakes of ≥MW 2 since 1850 in the Taupō District ................. 8 Figure 2.3 Ground-surface deformation from historical earthquake swarms in the Taupō District ................ 9 Figure 2.4 Paleoseismic and fault location (trench) sites in and surrounding the Taupō District ................. 11 Figure 2.5 Interpreted photograph of part of the Lilburn trench across the Kaiapo Fault ............................. 13 Figure 2.6 Schematic cross-section of a Taupō Rift fault showing multiple fault strands converging at depth onto a single master fault. .......................................................................................................... 14 Figure 2.7 Examples of natural exposures of the Poutu Fault Zone ............................................................ 15 Figure 2.8 Potential surface-rupture segments for the Waihi and Poutu fault zones ................................... 16 Figure 3.1 Examples of faults that have been extended or extrapolated (inferred) along-strike across areas where they have almost certainly been eroded away (e.g. by stream erosion) or buried by young stream sediments. ...................................................................................................................... 18 Figure 3.2 Components of the Fault Avoidance Zones ................................................................................. 21 Figure 3.3 Fault Avoidance Zones developed for the areas covered in LiDAR data ................................... 23 Figure 3.4 Fault Avoidance Zones developed for the areas covered in LiDAR data in the Tongariro Domain ................................................................................................................................................... 26 Figure 3.5 Fault Avoidance zones developed for the areas covered in LiDAR data in the southern Taupō Domain ............................................................................................................................ 29 Figure 4.1 Fault Awareness Areas developed for the Taupō District Council .............................................. 33 Figure 4.2 Fault Awareness Areas developed for areas not covered by LiDAR data in the Tongariro Domain ....................................................................................................................................... 36 Figure 4.3 Fault Awareness Areas developed for areas not covered by LiDAR data in the Taupō and Whakamaru domains ................................................................................................................. 38 Figure 4.4 Fault Awareness Areas developed for the eastern Taupō District .............................................. 40 Figure 5.1 Active faults in the Taupō District, overlain by summary (generalised) major faults in the 2010 version of the NSHM .................................................................................................................. 44 Figure 5.2 Schematic showing how recurrence intervals can vary for different traces on a Taupō Rift fault . 45 Figure 5.3 Examples of strike-slip ground-surface fault rupture in the