Proceedings of conference XLV; a workshop on Fault segmentation and controls of rupture initiation and termination

2005

The Hurunui section of the Hope Fault is a newly defined, 42 km long geomorphic fault section which extends from Harper Pass to the Hope-Boyle River confluence. Reconnaissance mapping along the Hurunui section from Hope Shelter to Harper Pass provided new data on its location, geomorphology, displacement, and slip rate. More than 200 previously published field observations of dextrally and vertically displaced landforms along the fault provide data on the distribution of displacement along the fault trace. Five radiocarbon dates found in association with offset geomorphic features are presented and two new measures of dextral slip rate are calculated. At McKenzie Stream, a late Holocene fan complex is cut by the Hope Fault. Young abandoned and active channels on this surface show dextral offsets of up to 22 ± 2 m along a south-facing scarp with a height of up to 5 m. Woody litter from a unit in this complex has yielded a radiocarbon age of 2331 ±55 yr BP and a corresponding minimum horizontal slip rate of 8.1-11.0 mm/yr. At Macs Knob, large dextral deflections of stream catchments are linked to episodes of glacial resetting of the landscape. Correlation of the offset of "Macs stream" (166 ± 17 m) with a post-Aranuian age peat (10 782 ± 60 yr BP) yields a maximum horizontal slip rate of 13.0 ± 1.5 mm/yr. The single-event dextral displacement, based on offset stream channels at McKenzie fan, is 3.2-3.8 m (av. c. 3.4 m). The ratio of dextral to vertical slip is c. 7 ± 2:1, indicating that the Hope Fault has a dominantly strikeslip sense of motion.The average recurrence interval for the last 5-7 events (i.e., to produce 19-24 m slip at McKenzie fan) is 310-490 yr. The age of the most recent surface-rupturing earthquake at this site is not known, though felt effects, fault scaling, and landscape arguments indicate it was not the AD 1888 North Canterbury earthquake.

Section: Fault Segmentation Magnitude and The Most Recent Earthquakementioning

confidence: 97%

Morphology and slip rate of the Hurunui section of the Hope Fault, South Island, New Zealand

Langridge¹,

2005

“…The basis for segmentation has been refined on the North and East Anatolian Fault systems in Turkey where both the historic rupture segmentation (i.e., segments) and geomorphic segmentation (i.e., sections) are quite well understood due to a long record of historic surface faulting events and ease of mapping distinct fault sections (Barka & Kadinsky-Cade Barka 1992;Ambraseys & Finkel 1995). Segments and sections have been defined in these regions, based on the continuity of strike along pieces of fault, and by their distinctly discontinuous beginning and endpoints, where surface faulting events may initiate or terminate (Schwartz & Sibson 1989;Lettis et al 2002). In this paper we use the terms segment and section with the intention of differentiating between parts of the fault that are inferred to represent past (and therefore possible future) individual surface ruptures ("segment"), from purely geographic parts that have structural and morphological changes at their endpoints ("section").…”

Section: Definition Of Geometric Fault Segmentationmentioning

confidence: 99%

“…A c. 2 km wide right side-step at Kaitoke forms the Kaitoke Basin, a small extensional stepover basin in a dextral-slip system. If large enough, such step-overs commonly result in the termination of surface fault ruptures (King & Nábělek 1985;Barka & Kadinsky-Cade 1988;Schwartz & Sibson 1989;Lettis et al 2002). The stepover is preceded by a strike change from c. 056° to 066° and progresses into a right step of 1.5-2 km, to two active strands at the southern end of the Tararua Range (Fig.…”

Section: The Wellington-hutt Valley Segmentmentioning

confidence: 99%

Defining the geometric segmentation and Holocene slip rate of the Wellington Fault, New Zealand: The Pahiatua section

Langridge¹,

Dissen

2005

slip rate, strike-slip fault sections; (2) produce multi-metre single-event dextral displacements; (3) have short recurrence intervals; and (4) individually have the capability to generate surface-rupturing earthquakes of M w > 7.Keywords Wellington Fault; fault segmentation; Pahiatua section; Tararua section; neotectonics; seismic hazard; slip rate; recurrence; NZMS 260 sheets S25, T24, T25 Abstract The Wellington Fault is a major active, right lateral, strike-slip fault in southern North Island that can be divided into three distinct geometric sections based on changes in neotectonic character and structural complexities. These are, from south to north: the Wellington-Hutt Valley segment; Tararua section; and Pahiatua section. The Pahiatua section is a 42 km long, straight, NNE-striking fault section defined between two geometric endpoints near Putara in the south and Woodville. This section has been mapped in detail and exhibits classic strike-slip tectonic geomorphology and late Quaternary dextral displacements of up to 125 m. Three trenches excavated at sites along the Pahiatua section are used to define the dextral slip rate for this section. At Bennett trench site, a stream is dextrally deflected 50 ± 6 m. Peaty silts underlying "deflected" channel deposits in the trench yield an age of 8390-8700 cal. yr BP, providing a minimum dextral slip rate of 5.1-6.7 mm/yr. At Hughes 1 site, a stream is deflected 60 ± 5 m. Peaty material found stratigraphically above the deflection there was dated (10 500-11 160 cal. yr BP), yielding a maximum slip rate of 4.9-6.2 mm/yr for this displacement. Ebbett 1 trench was excavated across the fault zone where a smaller displacement (18 ± 2 m) yielded a slip rate range of 3.2-5.2 mm/yr. Our preferred dextral slip rate (5.1-6.2 mm/yr) comes from the combination of the minimum and maximum rates from Bennett and Hughes 1 sites. This range is generally lower than (but slightly overlaps) that for the Wellington-Hutt Valley segment (6-7.6 mm/yr). The single-event displacement range for the Pahiatua section determined from field measurements is 4.5 ± 1 m. From this data we calculate a recurrence interval for surface-rupturing earthquakes of 564-1080 yr.The overlap of results from both the Pahiatua section and the Wellington-Hutt Valley segment allow us to assess the likely slip rate, single-event displacement, recurrence interval range, and characteristics of the 53 km long, bush-covered Tararua section of the Wellington Fault. The data show that both the Pahiatua and Tararua sections: (1) are moderate G04021;

“…Such a stepover would ordinarily be considered a barrier to rupture propagation in an analysis of seismic hazard based on mapped fault characteristics. Faultsegment rupture lengths are usually measured from one mapped geometric discontinuity (e.g., stepover, gap, bend, or intersection with other faults) to the next (e.g., Schwartz & Sibson 1989). This approach has proved useful in analysis of some strike-slip faults such as the Imperial Fault of California (e.g., Sieh 1996), and the North Anatolian Fault in Turkey (e.g., Barka & Kadinsky-Cade 1988), but would not have been able to describe the 1992 (M W 7.3) Landers earthquake in southern California, which ruptured across several pre-existing faults of different orientations and had significant stepovers and gaps along the surface rupture trace (Sieh et al 1993).…”

Section: Historical Surface Rupturesmentioning

confidence: 99%

Active faults, paleoseismology, and historical fault rupture in northern Wairarapa, North Island, New Zealand

Schermer

Dissen

et al. 2004

Active faulting in the upper plate of the Hikurangi subduction zone, North Island, New Zealand, represents a significant seismic hazard that is not yet well understood. In northern Wairarapa, the geometry and kinematics of active faults, and the Quaternary and historical surface-rupture record, have not previously been studied in detail. We present the results of mapping and paleoseismicity studies on faults in the northern Wairarapa region to document the characteristics of active faults and the timing of earthquakes. We focus on evidence for surface rupture in the 1855 Wairarapa (M W 8. Estimates of slip rates provided by these data suggest that a larger component of strike slip than previously suspected is occurring within the upper plate and that the faults accommodate a significant proportion of the dextral component of oblique subduction. Assessment of seismic hazard is difficult because the known fault scarp lengths appear too short to have accommodated the estimated singleevent displacements. Faults in the region are highly segmented, disconnected, and probably structurally immature, which implies that apparent geometric discontinuities at the surface may not be significant barriers to rupture propagation at depth and that the surface rupture record significantly under-represents the seismic slip on faults in the region.