Illustrations of historic and pre-historic surface rupture of active faults in New Zealand

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1 Illustrations of historic and pre-historic surface rupture of active faults in New Zealand R. Van Dissen, P.R., Wood, K. erryman, & S. Nathan Institute of Geological & Nuclear Sciences, Lower Hutt, New Zealand ASTRAT: Interim Guidelines for mitigating the impacts of building on, or near, active faults have recently been promulgated in New Zealand. In the Guidelines, the surface rupture hazard of an active fault is defined by the fault s average recurrence interval of surface rupture, and the complexity of its surface rupture trace. Examples of the latter are illustrated in this paper via a suite of photographs of historic and pre-historic surface ruptures of active faults in New Zealand. These images also highlight three important points relevant to the mitigation of surface rupture hazard: a) the location of past surface rupture along an active fault is generally a reliable guide as to the location of future surface rupture along the fault, b) surface rupture deformation is most intense at the fault, but, in places, significant off fault deformation can occur, and c) the extent of surface rupture deformation along an active fault can often be geographically defined to a level compatible with planning and engineering needs. 1 INTRODUTION The Ministry for the Environment, New Zealand, recently circulated Interim Guidelines for mitigating the impacts of building on, or near, active faults (Kerr at al. 2002, see also King et al. 2003). The aim of the Guidelines is to provide information about active faults, specifically fault rupture hazard, and to promote a risk-based approach when dealing with development in areas subject to fault rupture hazard. In the Guidelines, the surface rupture hazard of an active fault at a specific site is characterised by two parameters: a) the average recurrence interval of surface rupture of the fault, and b) the complexity of surface rupture of the fault. To aid in the implementation of planning controls along active faults in New Zealand, the Guidelines define the complexity of surface rupture deformation at a site through the use of the following terms: a) Well-defined: fault rupture deformation is well defined and of limited geographic width (e.g. metres to tens of metres wide). b) Distributed: fault rupture deformation is distributed over a relatively broad geographic width (e.g. tens to hundreds of metres wide), and typically comprises multiple fault traces and/or folds. c) Uncertain: the location of fault rupture deformation is uncertain usually because the fault has not been mapped in detail, or because evidence of deformation has been either buried or eroded away. This paper presents a suite of photographs of historic and pre-historic surface rupture of active faults in New Zealand that illustrate examples of fault trace complexity (i.e. well-defined and/or distributed fault rupture deformation). In doing so, we hope to place additional context on the nature and extent of fault rupture hazard in New Zealand, and to facilitate the use and application of the Guidelines. 2 EXAMPLES OF SURFAE RUPTURE ALONG ATIVE FAULTS IN NEW ZEALAND Figure 1 shows most of the known on-land active faults in New Zealand. The most hazardous of these, i.e. those with the shortest recurrence intervals of surface rupture, are highlighted in red (see Van Paper Number 156

2 Dissen et al. 2003). Figures 2-6 present photographic examples of surface rupture along New Zealand active faults. These photographs, along with accompanying references, underscore the following points relevant to the mitigation of surface rupture hazard, and the application of the Guidelines: a) The location of recent surface rupture along an active fault typically coincides with the location of past surface ruptures along the fault. Therefore, the location of past surface rupture deformation along an active fault is often a reliable guide as to the location of future surface rupture along the fault. b) Surface rupture deformation along an active fault is most intense at the fault, though significant off fault deformation can occur, and typically generates distinctive landforms. Thus, the likely geographic extent of future surface rupture deformation can often be defined to a level compatible with planning and engineering needs. These points underpin the fundamental basis for the development of the 1971 Alquist-Priolo Special Studies Zones Act in alifornia and the 2002 Interim Guidelines in New Zealand aimed at mitigating surface rupture hazard. REFERENES: eanland, S., erryman, K., lick, G Geological investigations of the 1987 Edgecumbe earthquake, New Zealand. N.Z. J. of Geol. & Geophys enson, A., Little, T., Van Dissen, R., Hill, N., Townsend, D Late Quaternary paleoseismic history and surface rupture characteristics of the eastern Awatere strike-slip fault, New Zealand. Geol. Soc. of America ull erryman, K Late Quaternary movement on the White reek fault, South Island, New Zealand. N.Z. J. of Geol. & Geophys owan, H The North anterbury earthquake of September 1, J. of the Royal Soc. of N.Z Grapes, R., Downes, G The 1855 Wairarapa, New Zealand earthquake analysis of historical data. ull. of the N.Z. National Soc. for Earthquake Engineering Grapes, R., Little, T., Downes, G Rupturing of the Awatere fault during the 1848 October 16 Marlborough earthquake, New Zealand: historical and present day evidence. N.Z. J. of Geol. & Geophys King, A.., runsdon, D.R., Shephard, R.., Kerr, J.E., Van Dissen, 2003, uilding adjacent to active faults: a risk-based approach. In proceedings, Pacific onference on Earthquake Engineering, hristchurch, New Zealand, February, 2003, Paper No.158. Kerr, J., Nathan, S., runsdon, D., King, A., Van Dissen, R Interim guidelines: Planning for development of land on or close to active faults. Institute of Geological & Nuclear Sciences lient Report 2002/124 (prepared for Ministry for the Environment, New Zealand). Lensen, G Late Quaternary Tectonic Map of New Zealand, sheets N28D, O28 and N29, Hillersden; sheets O28D, P28A and P28, Renwick, scale 1:50,000 (with notes), N.Z. Dep. Sci. and Ind. Res., Wellington, New Zealand. Norris, R., ooper, A Late Quaternary slip rates and slip partitioning on the Alpine Fault, New Zealand. J. Structural Geol Van Dissen, R.J., erryman, K., Webb, T., Stirling, M., Villamor, P., Wood, P.R., Nathan, S., Nicol, A., egg, J., arrell, D., McVerry, G., Langridge, R., Litchfield, N., Pace,., 2003, An interim classification of New Zealand s active faults for the mitigation of surface rupture hazards. In proceedings, Pacific onference on Earthquake Engineering, hristchurch, New Zealand, February, 2003, Paper No.155. Van Dissen, R., erryman, K Surface rupture earthquakes over the last c years in the Wellington region, New Zealand, and implications for ground shaking hazard. J. Geophys. Res Van Dissen, R., Hull, A., Read, S Timing of large Holocene earthquakes on the Ostler fault, South Island, New Zealand: J. Geodetic Soc. Japan. In proceedings, RM '93, Kobe, Japan: Zachariasen, J., erryman, K., Prentice,., Langridge, R., Stirling, M., Villamor, P., Rymer, M Size and timing of large prehistoric earthquakes on the Wairau fault, South Island. Institute of Geological & Nuclear Sciences lient Report 2001/13 (prepared for the Earthquake ommission, NZ EQ Research Project No 99/389). 2

3 ctive fault: average recurrence interval of surface rupture less than 2000 years Active fault: average recurrence interval greater than 2000 years or undefined km Figure 1. Known on-land active faults in New Zealand (for more information regarding the recurrence interval classifications of many of the above active faults, see Van Dissen et al. 2003). 3

4 Figure 2. Historic surface rupture: A) The 1987 Edgecumbe earthquake was associated with about 14 km of surface rupture along the Edgecumbe fault, and other related faults, and ) up to about 2 m of vertical displacement of the ground surface at the fault trace (eanland et al. 1989). Rupture often followed a preexisting fault scarp. In these two photographs, surface rupture deformation is generally well-defined, and its location is marked by the arrows. ) The 1929 Murchison earthquake was associated with over 4 m of vertical displacement of the ground surface at the White reek fault (erryman 1980). Note bicyclist standing on upthrown side of road that is displaced by the fault. (photos A & by D.L. Homer, N 9977/10 & 10115/37, respectively; photo, GNS collection). 4

5 D Figure 3. Historic surface rupture: A & ) The 1888 earthquake on the Hope fault was associated with up to about 3 m of right lateral displacement of the ground surface at the fault trace (the offset fence-line records the amount of displacement across the fault), and about 30 km of surface rupture along the fault (owan 1991). ) hanges in strike of the Hope fault at Glynn Wye correspond with changes in fault trace complexity from welldefined to distributed. & D) The 1855 earthquake on the Wairarapa fault was associated with over 100 km of surface rupture along the fault, and up to about 12 m of right-lateral displacement of the ground surface at the fault trace (Grapes & Downes 1997). D) Abandoned terraces of the Waiohine River are laterally displaced by progressively larger amounts with increasing age, up to a maximum of about 130 m, along the same well-defined fault trace that ruptured in 1855, indicating that multiple surface ruptures have occurred at the same location along the same fault trace. Arrows mark location of surface fault rupture. (photo A by A. McKay, GNS collection; photos -D by D.L. Homer, N 3602/26, 8414/22 & 123/b, respectively). 5

6 D Figure 4. Historic and pre-historic surface rupture. A & ) The 1848 earthquake on the eastern section of the Awatere fault was associated with over 100 km of surface rupture along the fault, and as much as about 7 m of right-lateral displacement of the ground surface at the fault trace (Grapes et al. 1998, enson et al. 2001). ) The most recent surface rupture of the Alpine fault in Westland was about 285 years ago and was associated with about 8 m of right lateral displacement at the fault and up to 400 km of rupture along the fault (Norris & ooper 2000). D) The most recent rupture along the well-defined trace of the Wairau section of the Alpine fault in Marlborough was about 2000 years ago, and was associated with about 5 m of right lateral displacement at the fault (Lensen 1976, Zachariasen et al. 2001). Arrows mark location of surface fault rupture. (photos A-D by D.L. Homer, N 3940/12, 4932/16, 6563/19 & 17871/24, respectively). 6

7 Figure 5. Pre-historic surface rupture. A & ) The most recent surface rupture of the Wellington-Hutt Valley section of the Wellington fault occurred about 400 years ago and was associated with as much as 5 m of right lateral displacement at the fault (Van Dissen & erryman 1996). ) Thoughtful subdivision and open-space layout ensured that houses were kept away from the well-defined trace of the Wellington fault through Totara Park. ) An example of the well-defined trace of the Wellington fault in the northern Wairarapa. Arrows mark location of surface fault rupture. (photos A- by D.L. Homer, N 7748/31, 14444/10 & 12946/9, respectively). 7

8 Figure 6. Pre-historic surface rupture. A-) Examples of the complex trace of the Ostler fault where surface rupture deformation, though concentrated at the fault, is also distributed over a relatively broad region of more than 100 m either side of the fault (Van Dissen et al. 1994). Arrows mark location of surface fault rupture. (photos A- by D.L. Homer, N 3418/a, N 576/b & GST 281/3, respectively). 8