MEANDER LOOP MIGRATION AND LIQUEFACTION SUSCEPTIBILITY: LIQUEFACTION ALONG THE HEATHCOTE RIVER DURING THE 2010-11 CANTERBURY EARTHQUAKE SEQUENCE A thesis submitted in partial fulfilment of the requirements for the degree of Master of Science in Geology at the University of Canterbury by KIERAN THOMAS GRACE 2015 ABSTRACT Spatial variations in river facies exerted a strong influence on the distribution of liquefaction features observed in Christchurch during the 2010-11 Canterbury Earthquake Sequence (CES). Liquefaction and liquefaction-induced ground deformation was primarily concentrated near modern waterways and areas underlain by Holocene fluvial deposits with shallow water tables (< 1 to 2 m). In southern Christchurch, spatial variations of liquefaction and subsidence were documented in the suburbs within inner meander loops of the Heathcote River. Newly acquired geospatial data, geotechnical reports and eye-witness discussions are compiled to provide a detailed account of the surficial effects of CES liquefaction and ground deformation adjacent to the Heathcote River. LiDAR data and aerial photography are used to produce a new series of original figures which reveal the locations of recurrent liquefaction and subsidence. To investigate why variable liquefaction patterns occurred, the distribution of surface ejecta and associated ground damage is compared with near-surface sedimentologic, topographic, and geomorphic variability to seek relationships between the near-surface properties and observed ground damages. The most severe liquefaction was concentrated within a topographic low in the suburb of St Martins, an inner meander loop of the Heathcote River, with liquefaction only minor or absent in the surrounding areas. Subsurface investigations at two sites in St Martins enable documentation of fluvial stratigraphy, the expressions of liquefaction, and identification of pre-CES liquefaction features. Excavation to water table depths (~1.5 m below the surface) across sand boils reveals multiple generations of CES liquefaction dikes and sills that cross- cut Holocene fluvial and anthropogenic stratigraphy. Based on in situ geotechnical tests (CPT) indicating sediment with a factor of safety < 1, the majority of surface ejecta was sourced from well-sorted fine to medium sand at < 5 m depth, with the most damaging liquefaction corresponding with the location of a low-lying sandy paleochannel, a remnant river channel from the Holocene migration of the meander in St Martins. In the adjacent suburb of Beckenham, where migration of the Heathcote River has been laterally confined by topography associated with the volcanic lithologies of Banks Peninsula, severe liquefaction was absent with only minor sand boils occurring closest to the modern river channel. Auger sampling across the suburb revealed thick (>1 m) clay-rich overbank and back swamp sediments that produced a stratigraphy which likely confined the units susceptible to liquefaction and prevented widespread ejection of liquefied material. ii This analysis suggests river migration promotes the formation and preservation of fluvial deposits prone to liquefaction. Trenching revealed the strongest CES earthquakes with large vertical accelerations favoured sill formation and severe subsidence at highly susceptible locations corresponding with an abandoned channel. Less vulnerable sites containing deeper and thinner sand bodies only liquefied in the strongest and most proximal earthquakes forming minor localised liquefaction features. Liquefaction was less prominent and severe subsidence was absent where lateral confinement of a Heathcote meander has promoted the formation of fluvial stratum resistant to liquefaction. Correlating CES liquefaction with geomorphic interpretations of Christchurch’s Heathcote River highlights methods in which the performance of liquefaction susceptibility models can be improved. These include developing a reliable proxy for estimating soil conditions in meandering fluvial systems by interpreting the geology and geomorphology, derived from LiDAR data and modern river morphology, to improve the methods of accounting for the susceptibility of an area. Combining geomorphic interpretations with geotechnical data can be applied elsewhere to identify regional liquefaction susceptibilities, improve existing liquefaction susceptibility datasets, and predict future earthquake damage. iii Table of Contents ABSTRACT ............................................................................................................................... ii TABLE OF CONTENTS .......................................................................................................... iv LIST OF FIGURES ................................................................................................................. vii LIST OF TABLES ..................................................................................................................... x ACKNOWLEDGEMENTS ...................................................................................................... xi CHAPTER 1 INTRODUCTION 1.1 INTRODUCTION ............................................................................................................... 1 1.1.1 Study background ................................................................................................. 1 1.1.2 Geotechnical data .................................................................................................. 5 1.1.3 Study focus............................................................................................................ 6 1.2 CHRISTCHURCH AND THE CANTERBURY EARTHQUAKE SEQUENCE .............. 7 1.2.1 Regional setting .................................................................................................... 7 1.2.2 Pre-CES earthquake history in Christchurch ...................................................... 11 1.2.3 Seismicity and epicenter migration ..................................................................... 11 1.3 LIQUEFACTION RESEARCH ........................................................................................ 14 1.3.1 Review of Christchurch liquefaction susceptibility prior to the CES ................. 15 1.3.2 Liquefaction surface manifestation ..................................................................... 20 1.3.3 Liquefaction susceptibility parameters ............................................................... 23 1.3.4 Meandering river geomorphology and liquefaction susceptibility ..................... 24 1.4 THESIS SCOPE................................................................................................................. 28 1.4.1 Thesis objectives ................................................................................................. 28 1.4.2 Thesis organization ............................................................................................. 29 CHAPTER 2 RESEARCH METHODS 2.1 INTRODUCTION ............................................................................................................. 31 2.2 REMOTE SENSING TECHNIQUES ............................................................................... 31 2.2.1 Mapping liquefaction distributions by aerial photography ................................. 31 2.2.2 Post-earthquake digital elevation analysis .......................................................... 31 iv 2.2.3 Geomorphic mapping by digital elevation model ............................................... 32 2.3 TRENCHING THROUGH LIQUEFACTION FEATURES ............................................ 33 2.3.1 Site selection and trench digging ........................................................................ 33 2.3.2 Trench logging .................................................................................................... 35 2.3.3 Radiocarbon dating ............................................................................................. 35 2.4 SEDIMENT ANALYSIS................................................................................................... 36 2.4.1 Trench and hand auger sampling ........................................................................ 36 2.4.2 Laser-Sizer grain size analysis ............................................................................ 37 2.4.3 Pipette clay analysis ............................................................................................ 38 2.5 GEOTECHNICAL DATA................................................................................................. 39 2.5.1 CPT ..................................................................................................................... 39 2.5.2 CLiq .................................................................................................................... 39 2.5.3 Hydrological conditions ...................................................................................... 39 2.6 GROUND ACCELERATION DATA ............................................................................... 40 2.7 SUMMARY ....................................................................................................................... 40 CHAPTER 3 MEANDER BEND GEOMORPHOLOGY AND CES SURFACE OBSERVATIONS 3.1 INTRODUCTION ............................................................................................................. 42 3.2 RIVER MIGRATION AND GEOMORPHOLOGY......................................................... 42 3.2.1 Channel migration and lateral accretion ............................................................. 42 3.2.2 Point bar development ........................................................................................ 44 3.2.3 Avulsion .............................................................................................................. 45 3.2.4 Implications for liquefaction .............................................................................. 47 3.3 CHRISTCHURCH SETTING ........................................................................................... 48 3.4 STUDY AREA .................................................................................................................. 49 3.4.1 Location and geomorphology ............................................................................. 49 3.4.2 Topography ......................................................................................................... 50 3.4.3 Ground water elevations ..................................................................................... 53 3.5 CES SURFACE OBSERVATIONS AND GROUND DEFORMATION OF THE STUDY AREA ........................................................................................................................ 55 3.5.1 Initial observations following the major CES events ......................................... 55 3.5.2 Spatial distribution of liquefaction features ........................................................ 56 v 3.5.3 Liquefaction-induced ground deformation ......................................................... 58 3.6 DISCUSSION .................................................................................................................... 61 3.6.1 Geomorphology and meander migration ............................................................ 61 3.6.2 Liquefaction distribution and facies control ....................................................... 64 3.6.3 Subsidence distribution and facies control ......................................................... 65 3.6.4 Lateral spreading distribution and facies control ................................................ 67 3.7 SUMMARY ....................................................................................................................... 69 CHAPTER 4 SUBSURFACE INVESTIGATIONS 4.1 INTRODUCTION ............................................................................................................. 70 4.2 SUBSURFACE INVESTIGATIONS IN ST MARTINS .................................................. 70 4.3 TRENCH SITE 1: ST MARTINS PARK .......................................................................... 71 4.3.1 Trench stratigraphy ............................................................................................. 74 4.3.2 Liquefaction features .......................................................................................... 74 4.3.3 Grain size analysis .............................................................................................. 78 4.4 TRENCH SITE 2: 68A ST MARTINS ROAD ................................................................. 79 4.4.1 Trench stratigraphy ............................................................................................. 82 4.4.2 Liquefaction features .......................................................................................... 84 4.4.3 Pre-CES liquefaction features ............................................................................. 91 4.4.4 Grain size analysis .............................................................................................. 94 4.5 SUBSUEFACE INVESTIGATIONS IN BECKENHAM ................................................ 96 4.5.1 Beckenham Park: Auger 1 .................................................................................. 96 4.5.2 70 Corson Ave: Auger 2 ..................................................................................... 99 4.5.3 Intersection of Waimea Tce and Eastern Tce: Auger 3 .................................... 100 4.5.4 Grain size analysis ............................................................................................ 101 4.6. CLAY ANALYSIS ......................................................................................................... 102 4.7. DISCUSSION ................................................................................................................. 105 4.7.1 Geologic evolution of the study area ................................................................ 105 4.7.2 Liquefaction expressions and site characteristics ............................................. 105 4.7.3 Seismologic triggering thresholds of CES liquefaction features ...................... 106 4.7.4 Paleoseismic implications ................................................................................. 108 4.7.5 CPT data............................................................................................................ 110 vi 4.7.6 Liquefaction characteristics as proxies for channel location ............................ 111 4.8 SUMMARY ..................................................................................................................... 111 CHAPTER 5 CONCLUSIONS 5.1 INTRODUCTION ........................................................................................................... 113 5.2 KEY FINDINGS .............................................................................................................. 113 5.2.1 The influence of meander migration on liquefaction susceptibility ................. 113 5.2.2 Comparison of St Martins and Beckenham meander loops .............................. 114 5.2.3 Comparison of the Heathcote River with the Avon River ................................ 115 5.3 FUTURE IMPLICATIONS ............................................................................................. 115 5.3.1 Landform controls on liquefaction.................................................................... 115 5.3.2 Geotechnical Investigations ............................................................................. 116 5.3.3 Land classification and building guidelines ...................................................... 117 5.3.4 Liquefaction susceptibility mapping ................................................................. 118 5.4 RESEARCH SUMMARY ............................................................................................... 120 REFERENCES ...................................................................................................................... 122 APPENDIX A ........................................................................................................................ 130 List of Figures Figure 1.1: Schematic cross-section of alluvial lithofacies at the apex of a meander ............... 2 Figure 1.2: Map of Christchurch’s river systems and the outline of the study area .................. 4 Figure 1.3: New Zealand Tectonic setting ................................................................................. 7 Figure 1.4: Geology of the Canterbury region ........................................................................... 9 Figure 1.5: Geological cross-section of Christchurch .............................................................. 10 Figure 1.6: Regional surficial geology, seismicity and fault location map of Canterbury ...... 14 Figure 1.7: Map of soil types susceptible to liquefaction from Elder et al. (1991) ................. 16 Figure 1.8: Liquefaction susceptibility of Christchurch from Brown & Weeber (1992) ........ 17 Figure 1.9: Map of liquefaction susceptibility zones from the Christchurch Engineering Lifelines Group (1997) ............................................................................................................ 18 vii Figure 1.10: Liquefaction susceptibility assessment for the Christchurch urban area for summer ground water levels from Clough (2005) ................................................................... 19 Figure 1.11: Liquefaction ejecta from the Christchurch earthquake ....................................... 20 Figure 1.12: Schematic vertical section of liquefaction features ............................................. 21 Figure 1.13: Schematic block diagram of complex ground deformation ................................ 22 Figure 1.14: Surface ejecta following scroll patterns of point bar deposits in the New Madrid seismic zone ............................................................................................................................. 26 Figure 1.15: Correlation of abandoned meanders and damage distributions in Dagupan City following the 1990 M 7.8 Luzon earthquake ......................................................................... 27 w Figure 1.16: Locations of the former Waimakariri River channels and liquefied zones following the Darfield earthquake ........................................................................................... 28 Figure 2.1: Locations of subsurface investigations across the study area ............................... 34 Figure 2.2: Excavated trench at Site 2 ..................................................................................... 34 Figure 2.3: Hand auger sample collection ............................................................................... 37 Figure 2.4: Photograph of the pipette analysis......................................................................... 38 Figure 3.1 Descriptive terminology of meander bends ............................................................ 43 Figure 3.2: Meander bend migration patterns .......................................................................... 44 Figure 3.3: Cross-section of point bar development ................................................................ 45 Figure 3.4: Aerial photographs of meandering rivers .............................................................. 46 Figure 3.5: Sedimentation model for channel fills of an avulsion abandoned channel ........... 47 Figure 3.6: Study area location ................................................................................................ 50 Figure 3.7: Topographic changes from LiDAR data ............................................................... 51 Figure 3.8: Hillshade image from LiDAR data ....................................................................... 53 Figure 3.9: Groundwater elevations ......................................................................................... 54 Figure 3.10: Damage to the St Martins library ........................................................................ 56 Figure 3.11: Mapped distribution of surface liquefaction features .......................................... 57 Figure 3.12: Differential LiDAR model of Christchurch ........................................................ 58 Figure 3.13: Differential LiDAR model the study area ........................................................... 59 Figure 3.14: Elevation histogram showing the total area of surface elevation change ............ 60 Figure 3.15: Geomorphic map of the study area...................................................................... 62 Figure 3.16: Historic photograph of St Martins ....................................................................... 63 Figure 3.17: Transects locations and CES liquefaction-induced subsidence plots from St Martins, Beckenham and Avondale ......................................................................................... 66 Figure 3.18: Horizontal movement vectors of the Avon River and the Heathcote Rivers ...... 68 viii Figure 4.1: The location of subsurface investigations ............................................................. 71 Figure 4.2: Site 1 and the location of the trench ...................................................................... 72 Figure 4.3: Detailed trench log and unit descriptions of the east wall and floor of Site 1....... 73 Figure 4.4: Photographs of liquefaction features at Site 1 ....................................................... 75 Figure 4.5: Thin liquefaction dike within the trench floor ....................................................... 76 Figure 4.6: The Factor of Safety against liquefaction plot near to Site 1 ................................ 77 Figure 4.7: Probabilistic grain sizes distribution curves of the fluvial stratigraphy and CES liquefaction features ................................................................................................................. 70 Figure 4.8: Site 2 and the location of the trench ...................................................................... 80 Figure 4.9: Detailed trench log and unit descriptions of the east wall at Site 2....................... 81 Figure 4.10: Trench logs of anthropogenic pits cross-cutting fluvial stratigraphy .................. 83 Figure 4.11: Trench log of anthropogenic pit cross-cutting fluvial stratigraphy ..................... 84 Figure 4.12: Propagation of liquefaction sill in the eastern wall ............................................. 85 Figure 4.13: Liquefaction sill at Site 2..................................................................................... 86 Figure 4.14: Liquefaction sill truncating a subvertical planar dike ......................................... 87 Figure 4.15: Liquefaction filled clay sewer pipe ..................................................................... 87 Figure 4.16: The Factor of Safety against liquefaction plot at Site 2 ...................................... 88 Figure 4.17: Mapped spatial distribution of liquefaction throughout the CES ........................ 90 Figure 4.18: Trench log of the northern end of the western wall at Site 2 .............................. 92 Figure 4.19: Pre-CES liquefaction dike ................................................................................... 93 Figure 4.20: Liquefaction deposits from Site 2 ....................................................................... 94 Figure 4.21: Probabilistic grain sizes distribution curves of the fluvial stratigraphy .............. 95 Figure 4.22: Locations of the auger sites in Beckenham ......................................................... 96 Figure 4.23: Soil profile from Beckenham Park ...................................................................... 97 Figure 4.24: The Factor of Safety against liquefaction plot near Beckenham Park ................ 98 Figure 4.25: Soil profile from 70 Corson Ave ......................................................................... 99 Figure 4.26: The Factor of Safety against liquefaction plot near 70 Corson Ave ................. 100 Figure 4.27: Soil profile from the intersection of Waimea Tce and Eastern Tce .................. 101 Figure 4.28: Probabilistic grain sizes distribution curves of the samples collected across Beckenham ............................................................................................................................. 102 Figure 4.29: PGA vs. M plot of major CES ......................................................................... 107 w Figure 4.30: Piezometer measurements following the M 5.3 13 June earthquake ............... 108 w ix List of Tables Table 1.1: Significant CES events and subsequent aftershocks .............................................. 12 Table 1.2: Liquefaction severity categories and expected surface observations ..................... 23 Table 4.1: Radiocarbon AMS results. ...................................................................................... 82 x