John Ristau

GNS Science · GeoNet

To understand the stress controls on the occurrence of a multi-fault rupture, we estimated the crustal stress between April 2013 to December 2018, i.e., before and after the Mw7.8 Kaikōura earthquake that occurred in New Zealand on 13 November 2016. We used both the focal mechanism solutions from the temporary seismic networks and the GeoNet moment...

Centroid Moment Tensor solutions (CMT’s) provide valuable information on the physics of an earthquake source, focal depth, and seismic moment. The earthquake rupture is described in terms of nine generalised force couples (a 3 × 3 matrix) that represent shear dislocation and volume change (see Jost and Herrmann 1989).

The determination of earthquake source parameters is of fundamental importance in seismological research. Moment tensor analysis involves fitting theoretical waveforms to observed broadband waveforms and inverting for the moment tensor elements, and allows for the calculation of focal mechanism (strike, dip, and rake), seismic moment (M0), moment m...

The Mw 7.8 Kaikōura earthquake ruptured at least 17 faults for a distance of approximately 165 km across the New Zealand plate boundary zone in the northeastern South Island. In the epicentral area, the earthquake produced displacement at the surface on The Humps, Leader, Conway‐Charwell, and Stone Jug faults, which are the primary focus of this ar...

Rapid assessment of a potentially destructive tsunami is critical if the tsunami travel-time is less than ~60 minutes. This is particularly important if the generative earthquake is distant enough that it is not felt strongly or not felt at all, or for a slow-rupture tsunami earthquake that does not generate high-frequency energy. To avoid false al...

The 2016 Mw 7.8 Kaikōura earthquake continued a notable decade of damaging earthquake impacts in New Zealand. The effects were wide ranging across the upper South Island, and included two fatalities, tsunami, tens of thousands of landslides, the collapse of one residential building, and damage to numerous structures and infrastructure. We present a...

We calculate stress drops for 176 earthquakes (M2.6-M6.6) from four sequences of earthquakes in New Zealand. Two sequences are within the subducting Pacific plate (Eketahuna, 2014, and Upper Hutt, 2005), one in the over-riding plate (Cook Strait, 2013), and one involved reverse faulting at the subduction interface (Pongaroa, 2015). We focus on obta...

In this study, a new local magnitude (ML) scale is developed for New Zealand and adjacent offshore regions. SeisComP3 (SC3) has been in use for earthquake analysis in New Zealand since September 2012 with the original Richter (1935) log A0 attenuation relationship for calculating ML. The attenuation characteristics of New Zealand differ significant...

We model regional stresses before and after the Mw 7.1 Darfield earthquake of September 2010 in Canterbury, New Zealand including crustal structure derived from seismic tomography. Models show that the Banks Peninsula volcanic assemblage acts as a strong, rigid block that pinches out ductile layers in the mid-crust but has little effect on shallowe...

The structure and kinematics of the continental intra-arc Taupo Rift have been constrained by fault-trace mapping, a large catalogue of focal mechanisms (N = 202) and fault-slip striations. The mean extension direction of ~137° is approximately orthogonal to the regional trend of the rift and arc front (α = 84° and 79° respectively) and to the stri...

New Zealand is one of the more seismically active countries in the world with over 15,000 earthquakes each year in New Zealand and the adjacent offshore region. Routine regional moment tensor (RMT) analysis was implemented by GeoNet in 2007, and nearly 1300 RMT solutions have been calculated for the New Zealand region from August 2003 through early...

Tsunami science has evolved considerably in the last two decades due to technological advancements which also helped push for better numerical modelling of the tsunami phases (generation to inundation). The deployment of DART® buoys has also been a considerable milestone in tsunami forecasting. Tsunami forecasting is one of the parts that tsunami m...

The Pegasus Bay aftershock sequence is the most recent aftershock sequence of the 2010 September 3 UTC moment magnitude (Mw) 7.1 Darfield earthquake in the Canterbury region of New Zealand. The Pegasus Bay aftershock sequence began on 2011 December 23 UTC with three events of Mw 5.4–5.9 located in the offshore region of Pegasus Bay, east of Christc...

Reliable determination of earthquake source parameters is a subject of fundamental importance for seismological research. It also provides critical observational constraints to the study of deformation and stress within the lithosphere. A comprehensive catalog of earthquake source parameters is not only essential to the understanding of global and...

Potentially active faults are exposed in the steep glaciated topography of the central Southern Alps, New Zealand, immediately adjacent to the Alpine Fault plate boundary. Four major faults exposed along the flanks of three of the highest mountain ranges strike 10-23 km (potentially 40 km) NNE oblique to the Alpine Fault, dipping 57° ± 12° NW in th...

A moment magnitude (Mw) 6.2 earthquake struck beneath the outer suburbs of Christchurch, New Zealand's second largest city, on 22 February 2011 local time. The Christchurch earthquake was the deadliest in New Zealand since the 1931 Mw 7.8 Hawkes Bay earthquake and the most expensive in New Zealand's recorded history. The effects of the earthquake o...

On 22 February 2011 New Zealand time (21 February UTC), the MW 6.2 Christchurch earthquake occurred just 7 km southeast of the center of Christchurch city, New Zealand (Fry et al. 2011, Holden 2011, page 783 of this issue). There were 181 confirmed fatalities, and the damage to Christchurch city is estimated to be NZ$15 billion–$NZ20 billion (US$12...

Large earthquakes within seismogenic crust are generally thought to require the pre-existence of large fault structures. Such fault structures appear to evolve by the progressive growth and amalgamation of smaller faults and fractures (Cowie and Scholz 1992). In the course of their evolution some components of an evolving fault system may be inheri...

Relocated upper mantle seismicity, using a 3D velocity model, delineates three tightly clustered (about 12km diameter) zones of seismicity that occur in the mantle wedge under the fore-arc region of the northern Hikurangi margin, North Island, New Zealand. These clusters extend from the subducting plate at about 55km depth up to about 35km, and coi...

At 04:35 on Saturday 4 September 2010 local time (16:35 on 3 September UT) a moment magnitude ( Mw ) 7.1 earthquake struck approximately 10 km southeast of the town of Darfield and within 40 km of New Zealand's second largest city, Christchurch, causing extensive damage in the city and surrounding region. There was no loss of life due to a fortunat...

The northern Canadian Cordillera is remarkably tectonically and seismically active, extending from a terrane collision zone on the continental margin to an active fold and thrust belt at the eastern mountain front. The source and distribution of the deformation are constrained by (i) precision global positioning system (GPS) measurements; (ii) the...

More than 180 regional moment tensor (RMT) solutions for moderate-sized earthquakes (M ≥ 4) are used to examine the contemporary stress regime of western Canada and provide valuable information relating to earthquake hazard analysis. The overall regional stress pattern shows mainly NE–SW-oriented P axes for most of western Canada with local variati...

### Tectonic Settings & Seismicity in New Zealand New Zealand's active tectonics are dominated by the oblique convergence of the Pacific plate and the Australian plate, which produces earthquakes, volcanoes, active geological deformation, and steep terrain. The tectonic setting (Figure 1) makes New Zealand one of the most seismically active countr...

The M w 7.1 Darfield earthquake has provided geologists, geodesists and seismologists with well constrained surface fault rupture extent and displacements, densely spaced GPS coseismic displacements, striking InSAR images, and a globally unprecedented set of near-source strong motion data. Collectively, these datasets indicate that the Darfield ear...

The Darfield moment magnitude (M w) 7.1 earthquake of September 2010 is the first heavily damaging earthquake to strike New Zealand since the surface wave magnitude (M S) 7.8 Hawkes Bay earthquake in 1931. Although the earthquake has a clear strike-slip surface expression characterised by the Greendale Fault, seismological evidence suggests it is a...

The Mw 7.6 Dusky Sound earthquake of July 15th, 2009, was the largest magnitude earthquake in New Zealand since the devastating 1931 Hawke’s Bay event (Ms 7.8). The earthquake was sufficiently large to generate at least a 2.3 m wave at Passage Point. Despite its large magnitude, this event resulted in relatively minimal damage when compared to worl...

The Mw 7.6 Dusky Sound earthquake of July 15th, 2009, was the largest magnitude earthquake in New Zealand since the devastating 1931 Hawke‟s Bay event (Ms 7.8). The earthquake was sufficiently large to generate at least a 2.3 m wave at Passage Point. Despite its large magnitude, this event resulted in relatively minimal damage when compared to worl...

Slow slip events (SSEs) at the Hikurangi subduction margin adjacent to the North Island, New Zealand display a remarkable diversity of characteristics. Long duration (1-2 years), deep (40-60 km depth), large events (equivalent to Mw ~7.0) occur at the southern Hikurangi margin, while shallow (10-15 km depth), short (1-2 weeks), smaller events (equi...

Crustal seismic reflection data across the eastern Bay of Plenty and Raukumara Peninsula margin image an intriguing localised zone of strong reflectivity at a depth of about 35 - 40 km (12 - 16 s twt), that coincides with a local increase in seismicity. The zone lies between the Hikurangi subduction zone along eastern North Island and the extension...

New Zealand is one of the more seismically active countries in the world, with more than 15,000 earthquakes located each year. Routine moment tensor analysis of regional seismic data for earthquakes with moment magnitude Mw > similar to 3.5-4.0 has recently been implemented in New Zealand. Nearly 330 regional moment tensor (RMT) solutions have been...

The M w 6.7 George Sound earthquake of October 15, 2007, occurred only a few kilometres offshore of Fiordland, within a region where the subduction zone of the Australian Plate beneath the Pacific Plate intersects the offshore extension of the Alpine Fault. Rapid response deployments of portable seismographs, a strong motion recorder and GPS receiv...

At 9:22 pm local time on 15 July 2009 the largest earthquake in New Zealand for 80 years occurred in the southern Fiordland subduction zone in the southwest of the South Island. The earthquake ruptured the interface between the subducting Australian plate and overlying Pacific plate, with the deeper end of the rupture underlying the Fiordland coast...

SUMMARY Gisborne city experienced recorded peak ground accelerations exceeding 0.25g for the third time since 1966 in the magnitude Mw 6.6 earthquake at 075516 UT (8:55 pm local time) on 20 December 2007. The earthquake was at a hypocentral distance of 64 km from Gisborne at a depth of 40 km, well within the mantle of the subducted slab of the Paci...

The active tectonics of New Zealand are dominated by three main features (figure 1). Beneath the North Island there is active subduction of the Hikurangi trough where the Pacific plate is undergoing oblique subduction beneath the Australian plate at ∼ 45 mm/yr ( e.g. , Demets et al. 1990; Demets et al. 1994). The Hikurangi trough extends from the K...

Our ability to accurately locate crustal earthquakes has markedly improved with recent improvements in the density of temporary and permanent arrays, and with new approaches for relative earthquake location, using cross-correlation analysis and double-difference location techniques. If these approaches are applied to earthquake swarm sequences, suc...

Local magnitude (ML) is the primary magnitude scale calculated for western Canada by the Geological Survey of Canada (gsc). Moment magnitude (Mw), derived from moment tensor analysis, provides a more robust estimate of the magnitude of earthquakes but is more demanding to calculate. Moment tensor analysis of regional seismic data for earthquakes wi...

The Slave - Northern Cordillera Lithospheric Evolution (SNORCLE) corridors of the northern Cordillera sample some of the most, and least, seismically active regions of Canada. The earthquake history of this region is short. Precise determination of earthquake locations and depths is not possible even today. Nonetheless, significant gains in our kno...

The W.M. Keck Foundation is supporting a five-year program to conduct prototype seafloor observatory experiments to monitor the relationships between episodic deformation, fluid venting and microbial productivity on the Endeavour segment of the Juan de Fuca Ridge and at the intersection of the Nootka fault and the Cascadia subduction zone. At the E...

The W.M. Keck Foundation with additional support from the Monterey Bay Aquarium Research Institute (MBARI) and the University of Washington is supporting a five-year program to conduct prototype seafloor observatory experiments to constrain the relationships between episodic geological deformation, fluid venting and microbial productivity along the...

Moment tensor analysis of regional earthquakes (distances 3.5-4.0 in and near western Canada. This has resulted in about 10 times as many solutions per year for this region than have been calculated with teleseismic methods which are limited to earthquakes about M > 5.0. To date, more than 370 RMT solutions have been calculated for western Canada a...

Thesis (Ph.D.)--University of Victoria, 2004. Includes bibliographical references.

Local magnitude (ML) values of earthquakes off Canada's west coast are known to be underestimated by at least 0.5 magnitude units compared with other magnitude scales. Moment magnitude (Mw), derived from moment tensor analysis, provides the most robust estimate of the magnitude of earthquakes. Moment tensor analysis of regional seismic data in west...

Moment tensor analysis of regional seismic data (~ 1000 km or less) in western Canada and southeast Alaska, primarily the coastal and offshore region of British Columbia, has recently become possible due to the installation of more than 35 three-component broadband stations in western Canada, the U.S. Pacific northwest, and southeast Alaska. Region...

Moment tensor analysis of regional seismic data ( ~ 1000 km or less) in the coastal and offshore region of British Columbia (B.C.) has recently become possible due to the installation of more than 25 three-component broadband stations in B.C. and northwest Washington. This region is a tectonically active area consisting of the Pacific, North Americ...

Random noise is often a problem in geophysical data visualization because it obscures fine details and complicates identification of image features. Adaptive filters have recently been used to suppress speckle (random) noise in synthetic aperture radar (SAR) images. SAR data are similar to seismic reflection data, both in their data acquisition app...

A geophysical survey was performed at Sylvan, Manitoba, Canada (51°5′N, 97°22′W) to investigate a Lower Cretaceous kaolinite deposit. The deposit consists of zones of kaolinite, silica sand, and lignitic clay located in a series of channels formed during karsting of the underlying Palaeozoic bedrock and is covered by 3 to 5 m of glacial drift. The...

Space-borne Synthetic Aperture Radar (SAR) techniques have recently become one of the most flexible and cost-effective Earth-observation tools for monitoring surface processes, including natural hazard monitoring and management tasks such as landslides, volcanic activities, and earthquake-related problems. This study investigates the feasibility of...