The Kerepehi Fault, Hauraki Rift, North Island, New Zealand: Active Fault Characterisation and Hazard
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New Zealand Journal of Geology and Geophysics ISSN: 0028-8306 (Print) 1175-8791 (Online) Journal homepage: http://www.tandfonline.com/loi/tnzg20 The Kerepehi Fault, Hauraki Rift, North Island, New Zealand: active fault characterisation and hazard M Persaud, P Villamor, KR Berryman, W Ries, J Cousins, N Litchfield & BV Alloway To cite this article: M Persaud, P Villamor, KR Berryman, W Ries, J Cousins, N Litchfield & BV Alloway (2016) The Kerepehi Fault, Hauraki Rift, North Island, New Zealand: active fault characterisation and hazard, New Zealand Journal of Geology and Geophysics, 59:1, 117-135, DOI: 10.1080/00288306.2015.1127826 To link to this article: http://dx.doi.org/10.1080/00288306.2015.1127826 View supplementary material Published online: 04 May 2016. Submit your article to this journal View related articles View Crossmark data Citing articles: 1 View citing articles Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=tnzg20 Download by: [GNS Science] Date: 05 May 2016, At: 15:54 NEW ZEALAND JOURNAL OF GEOLOGY AND GEOPHYSICS, 2016 VOL. 59, NO. 1, 117–135 http://dx.doi.org/10.1080/00288306.2015.1127826 RESEARCH ARTICLE The Kerepehi Fault, Hauraki Rift, North Island, New Zealand: active fault characterisation and hazard M Persauda, P Villamorb, KR Berrymanb, W Riesb, J Cousinsb, N Litchfieldb and BV Allowayc aNatural Hazards Division, OMVAktiengesellschaft, Vienna, Austria; bGNS Science, Lower Hutt, New Zealand; cSchool of Geography, Environment and Earth Sciences, Victoria University of Wellington, Wellington, New Zealand ABSTRACT ARTICLE HISTORY The Kerepehi Fault is an active normal fault with a total onshore length of up to 80 km Received 29 June 2015 comprising six geometric/rupture segments, with four more offshore segments to the Accepted 11 November 2015 north. For the last 20 ± 2.5 ka the slip rate has been 0.08–0.4 mm a–1.Averagefault KEYWORDS rupture recurrence intervals are 5 ka or less on the central segments and 10 ka or more on Active faulting; earthquake- low slip rate segments to the north and south. Characteristic earthquakes for a single M M related damage; Hauraki segment rupture range from w 5.5 to 7.0, and up to w 7.2 or 7.4 in the unlikely event of Plains; Hauraki Rift; Kerepehi ruptureofalltheonshorefaultsegments. Fault rupture would result in damage to Fault; LiDAR; major unreinforced masonry buildings, chimneys and parapets in Auckland (45 km nearest earthquake occurrence; distant). Very severe damage to buildings in towns within the Hauraki Plains without paleoseismology specific seismic design (those built before 1960) may pose a significant risk to life and livelihood. Introduction The aim of this study is to document the location of active traces of the Kerepehi Fault and to derive the The Kerepehi Fault, in the Hauraki Plains region of magnitude of earthquakes associated with surface northern North Island, New Zealand, is a NNW-trend- rupture and their recurrence. We assess the rupture ing active normal fault (Figure 1). The Kerepehi Fault history of each of the main on-land strands of the and its offshore extension in the Hauraki Gulf has fault using tectonic geomorphology and paleoseismol- received some attention in previous studies related to ogy studies. We have used a high-resolution digital geological mapping (Houghton & Cuthbertson 1989), elevation model (DEM) derived from LiDAR data to active faulting and earthquake hazard (de Lange & map the faults, and traditional paleoseismic trenching Lowe 1990; Stirling et al. 2012; Litchfield et al. 2014), techniques combined with radiocarbon dating to and tsunami hazard (Chick et al. 2001). These studies assess the earthquake history and derived potential characterised the fault as a series of right-stepping en earthquakemagnitudes(seeTableS1formoredetails echelon traces ranging in length from 10 to 43 km of methods). From these data we obtain an indication with step-overs ranging from 3 to 6 km. Recent access of ground-shaking effects, and possible damage in Downloaded by [GNS Science] at 15:54 05 May 2016 to LiDAR (light detection and ranging) data has major population centres of northern North Island, revealed a far more complex pattern of Holocene associated with large earthquakes on the Kerepehi fault traces displacing the alluvial terrace surfaces of Fault. the Hauraki Plains than earlier appreciated. Whereas earlier mapping suggested relatively simple fault strands, the LiDAR-based interpretation indicates a Geologic and tectonic setting surface faulting pattern very similar in terms of density The Hauraki Rift and complexity to that described from the Taupo Rift (e.g. Villamor & Berryman 2001; Berryman et al. The Kerepehi Fault is located within the Hauraki Rift, 2008). Typically there are one or two main strands in a half-graben which extends from the Taupo Rift each segment and a myriad of generally shorter sec- NNW towards the Hauraki Gulf (Figure 1) separating ondary strands that splay from, or are parallel to, the the Coromandel Peninsula and Great Barrier Island main strands. The Kerepehi Fault is the most northerly from the Auckland and Northland Peninsula. The active fault in New Zealand with clear evidence for Hauraki Rift is c. 20–40 km wide and c. 250 km activity in the Holocene; it therefore makes a contri- long (Hochstein & Nixon 1979; Hochstein et al. bution to seismic hazard in large northern North Island 1986;deLange&Lowe1990; Hochstein & Ballance cities including Auckland, Hamilton and Tauranga. 1993), and comprises three distinct sections from CONTACT P Villamor [email protected] Supplementary material available online at www.tandfonline.com/10.1080/00288306.2015.1127826 © 2016 GNS Science 118 M PERSAUD ET AL. Downloaded by [GNS Science] at 15:54 05 May 2016 Figure 1. A, Location of the Hauraki Rift on the North Island of New Zealand with respect to the Taupo Rift (dashed grey rectangle) and the Hikurangi Subduction Zone. B, Location of main onshore active fault traces (red lines) and offshore active faults (dashed black lines) mapped prior to this study. All mapped traces are dipping to southwest. Onshore traces in the Hauraki Depression belong to the Kerepehi Fault. WNF is the Wairoa North Fault, the only other active fault known in the region (Wise et al. 2003). Offshore traces were mapped by Chick et al. (2001). Also plotted is the location of earthquakes with Mw >3.0 for the historic period until May 2015. The largest recent event is the 1972 Mw 5.1 Te Aroha earthquake. north to south: the Hauraki Gulf, the Firth of Thames active central-depression normal fault (Figure 2). The and the onshore Hauraki Depression (Figure 1). western boundary is formed by a minor hinge fault, The Hauraki Rift has been active since late Neogene the Firth of Thames Fault (Hochstein & Nixon 1979; time (Hochstein & Nixon 1979; Davidge 1982) before de Lange & Lowe 1990)(Figure 2). rifting shifted to the Taupo Rift at c. 2–3Ma(Figure Numerous hot springs occur within the Hauraki 1; Wilson & Rowland 2016). The Hauraki Rift is situ- Depression. Hochstein and Nixon (1979) calculated, ated in the back-arc of the Hikurangi subduction mar- from geothermometry of the springs, that an anoma- gin, parallel to the now-extinct volcanic arc of the lously high heat flow exists below the southern part Coromandel (Hochstein & Ballance 1993). Our study of the rift. This suggests that there is an upper mantle area, the Hauraki Depression, contains two main swell below the Hauraki Depression (Davidge 1982), NNW-striking normal faults: the now-inactive Haur- indicating thinned crust in this region. aki Fault at the foot of the Kaimai Ranges at the eastern Present-day seismic activity in the region is diffuse, margin of the depression; and the Kerepehi Fault, an but with a concentration in the central and southern NEW ZEALAND JOURNAL OF GEOLOGY AND GEOPHYSICS 119 Downloaded by [GNS Science] at 15:54 05 May 2016 Figure 2. Active fault traces of the Hauraki Rift, mapped here using a high-resolution DEM derived from LiDAR on a background geology map of the Hauraki Rift (simplified from Edbrooke 2001). Note that faults dipping to the southwest and the northeast are in red and grey-blue, respectively. Base map is a low-resolution DEM from LINZ. Shorelines are also mapped with LiDAR-DEM (see full DEM in Figure S2). Shore line 3 corresponds to that mapped by Schofield (1976). Solid black diamonds represent the location of trenches. Dark red numbers show the fault scarp heights (m). Black transverse lines are location of topographic profiles presented in Figure 3. Offshore fault segment is from Chick et al. (2001). M – Hauraki Depression (Figure 1). Most earthquakes in the with L 0.3 1.2 located between Te Aroha and Mor- region have focal depths of ≤12 km. In a microearth- rinsville at depths of ≤10 km and concluded that the quake survey, Backshall (1982) recorded 21 earthquakes nature of the macro- and microearthquake activity 120 M PERSAUD ET AL. Figure 3. Topographic transects across the Hauraki Rift showing location of active faults and measurement of fault throw. The throw range represents the maximum and minimum values taking into account maximum and minimum surface tilt and uncer- tainties due to erosion of terrace surfaces. Note the eastwards tilting of the Hinuera surfaces (H is Hinuera C of Manville and Wilson, 2004) on the footwall of the main strands of fault segments. Downloaded by [GNS Science] at 15:54 05 May 2016 beneath the Hauraki Plains is typical of an active con- Geological setting and geochronological tinental rift. The largest recent earthquake was the 1972 markers within the Hauraki Depression Te Aroha earthquake of M 5.2 (Adams et al. 1972) w The Hauraki Depression is surrounded by volcanic and (Figure 1).