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The Basin and Range hosted large pluvial lakes during the Pleistocene, which generally reached highstands following the Last Glacial Maximum and then regressed rapidly to near-modern levels. These lakes were large and deep enough to... more
The Basin and Range hosted large pluvial lakes during the Pleistocene, which generally reached highstands following the Last Glacial Maximum and then regressed rapidly to near-modern levels. These lakes were large and deep enough to profoundly affect the crust through flexure; they filled basins formed by faults, and they locally modified pore pressure and groundwater conditions. A compilation of geochronologic constraints on paleoshorelines and paleoseismicity suggests temporal correlations between lake level and earthquake recurrence, with changes in earthquake rates as lakes regressed. In the northwestern Basin and Range, climatic and tectonic conditions differ from the rest of the province: The modern and glacial climate is/was cooler and wetter, glacial lakes were proportionally larger, and the crustal strain rate is lower. Numerous valleys host late Pleistocene and Holocene fault scarps and evidence of >Mw 7 earthquakes in the last 15,000 yr. We compiled detailed lake hydro...
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Research Interests: Geology and Seismology
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Research Interests: Geology, Geochemistry, Geophysics, Pleistocene, Holocene, and 3 moreRadiocarbon Dating, Bedrock, and geosphere
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ABSTRACT The Alpine Fault is a major continental transform fault that delineates the boundary of the Australian and Pacific plates across the South Island of New Zealand. Although the fault has not ruptured during the short ~ 200 yr... more
ABSTRACT The Alpine Fault is a major continental transform fault that delineates the boundary of the Australian and Pacific plates across the South Island of New Zealand. Although the fault has not ruptured during the short ~ 200 yr history of European settlement, paleoseismic evidence shows it is capable of producing damaging (M > 7.5) earthquakes. To date, key physical and seismic properties of the fault, such as geometry, slip-rates, and dip, have been determined or inferred from surface outcrops, geomorphology, shallow boreholes, and/or trenches. High-resolution geophysical imaging at greater depths can extend and enhance interpretations of fault-zone structure and behaviour. We previously presented high-resolution 2-D and 3-D ground-penetrating radar images across a northern section of the fault that revealed multiple fault strands in the subsurface. We now describe the results of a high-resolution 3-D seismic survey to elucidate fault-zone structure to a depth of ~ 150 m. Careful tailored processing schemes were needed to address the following challenges presented by these data: i) significant static shifts caused by both topography and strong near-surface velocity heterogeneity, ii) substantial source-generated noise typical of very shallow seismic surveys, and iii) the imaging of complex, discontinuous, and dipping structures associated with the fault zone. We image a prominent reflection from the late Pleistocene basement surface that is juxtaposed on either side of the fault. Three-dimensional mapping of this surface reveals significant vertical offset (~ 35 m) across the main fault strand. In addition, distributed deformation within ~ 80 m of the main fault trace is evident in the form of normal fault drag on this surface. Joint interpretation of the GPR and seismic datasets allows the main fault strand and subsidiary faults within the overlying late Quaternary sediments to be traced from the near-surface to greater depth. The distribution of deformation across the shallow fault zone suggests greater slip at depth than that traditionally measured by offset of localised markers close to the surface.
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This study focuses on the identification and seismic characterization of the San Mateo fault, herein described for the first time. This fault is located in the central part of the Acambay graben, central Mexico. It is a 13 km long active... more
This study focuses on the identification and seismic characterization of the San Mateo fault, herein described for the first time. This fault is located in the central part of the Acambay graben, central Mexico. It is a 13 km long active normal fault with E-W direction and dip to the south. Two trenches were excavated in the locality of La Lechuguilla to determine the recent chronology of paleoearthquakes along this fault and to estimate its seismic parameters. At least three paleo-breaks have been found in one of these trenches and new radiocarbon ages indicate that they occurred from Late Pleistocene to the Holocene times. The oldest event (Event 1) occurred in 31.0-29.3 ky cal BP. Event 2 occurred in 19.1–6.5 ky cal BP and the younger faulting (Event 3) in 6.0 to 4.2 cal ky BP. These results suggest a recurrence interval of surface ruptures of about 11.57 5.32 ky. A slip rate of 0.085 0.025 mm / year and a magnitude (Mw) of 6.43 to 6.76 is estimated from the maximum coseismic dis...
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High‐resolution, three‐dimensional (3‐D) measurements of surface displacements during earthquakes can provide constraints on fault geometry and near‐surface slip and also quantify on‐fault and off‐fault deformation. However, measurements... more
High‐resolution, three‐dimensional (3‐D) measurements of surface displacements during earthquakes can provide constraints on fault geometry and near‐surface slip and also quantify on‐fault and off‐fault deformation. However, measurements of surface displacements are often hampered by a lack of high‐resolution preearthquake elevation data, such as lidar. For example, preearthquake lidar for the 2016 MW 7.8 Kaikōura, New Zealand, earthquake only covers ≲10% of ~180 km of mapped surface ruptures. To overcome a lack of preearthquake lidar, we measure 3‐D coseismic displacements during the Kaikōura earthquake using point clouds generated from aerial photographs. From these point clouds, which cover the whole area of the 2016 surface ruptures, it is possible to measure 3‐D displacements to within ±0.2 m. We measure coseismic slip and estimate the geometries of faults in the steep, inaccessible Seaward Kaikōura mountains, where postearthquake field observations are very sparse. The Jordan ...
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Differential lidar reveals unusual fault characteristics within a complex earthquake.
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The evolution of the continental intraarc Taupo Rift in the North Island, New Zealand, is rapid, significantly faster than comparative intracontinental rifts such as the African Rifts. Based on our faulting data and published geological,... more
The evolution of the continental intraarc Taupo Rift in the North Island, New Zealand, is rapid, significantly faster than comparative intracontinental rifts such as the African Rifts. Based on our faulting data and published geological, geophysical, and borehole data, we show that activity in the ~2 Ma Taupo Rift has rapidly and asymmetrically narrowed via inward and eastward migration of faulting (at rates of approximately 30 km Myr−1 and 15 km Myr−1, respectively) and has propagated southward along its axis ~70 km in 350 kyr. The loci of voluminous volcanic eruptions and active faulting are correlated in time and space, suggesting that a controlling factor in the rapid rift narrowing is the presence of large shallow heterogeneities in the crust, such as large rhyolitic magma bodies generated by subduction processes, which weaken the crust and localize deformation. Eastward migration of faulting also follows the eastward migration of the volcanic arc which may be related to rollba...
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The Acambay graben is part of the Trans-Mexican Volcanic Belt (TMVB) which strikes ESE-WNW across central Mexico. The belt is an active, calc-alkaline volcanic arc that is related to the subduction of the Rivera and Cocos plates... more
The Acambay graben is part of the Trans-Mexican Volcanic Belt (TMVB) which strikes ESE-WNW across central Mexico. The belt is an active, calc-alkaline volcanic arc that is related to the subduction of the Rivera and Cocos plates underneath the North American plate (e.g. Suter et al. 1995). The TMVB comprises a series of intra-arc basins that form the Chapala-Tula fault
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Shallow, crustal normal-faulting earthquakes represent a significant seismic risk to the local towns and regional cities of central Mexico. Within the Acambay graben, the Pastores Fault is a c. 33 km long active, east-west striking,... more
Shallow, crustal normal-faulting earthquakes represent a significant seismic risk to the local towns and regional cities of central Mexico. Within the Acambay graben, the Pastores Fault is a c. 33 km long active, east-west striking, north-dipping normal fault. Two paleoseismic trenches were excavated at the Manto del Rio site to estimate preliminary active fault and seismic hazard parameters. Both trenches showed evidence for at least two latest Pleistocene to Holocene paleo-earthquake ruptures, constrained by radiocarbon dates from the West trench and through correlation of pyroclastic units between the trenches. The oldest faulting event (Event III) is bracketed within the interval c. 31.5-41.0 cal kyr BP. Units higher in the trench are less displaced and provide evidence for at least one younger event. Rupture event II is bracketed within the interval c. 23.9-34.6 cal kyr BP. The youngest faulting event (Event I; 12.2-12.6 cal kyr BP) is inferred from the presence of organic infi...
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Research Interests: Geology, Geophysics, Seismology, Active Tectonics, Holocene, and 3 moreNew Zealand, Late Holocene, and Zealand
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ABSTRACT The Acambay graben is part of the Trans-Mexican Volcanic Belt (TMVB) which strikes ESE-WNW across central Mexico, where the major part of the Mexican population is concentrated. The TMVB is an active, calc-alkaline volcanic arc... more
ABSTRACT The Acambay graben is part of the Trans-Mexican Volcanic Belt (TMVB) which strikes ESE-WNW across central Mexico, where the major part of the Mexican population is concentrated. The TMVB is an active, calc-alkaline volcanic arc that is related to the subduction of the Rivera and Cocos plates underneath the North American plate. The TMVB contains a series of intra-arc basins that form the Chapala-Tula fault zone (450 km long, 50 km wide). One of these extensive basins, the Acambay graben, is 80 km long and 15 to 30 km wide. It is limited north by the E-W striking Epitacio-Huerta (EHF) and Acambay-Tixmadejé normal faults and south by the Venta de Bravo (VBF) and the Pastores faults (PF) in the south. Other minor active faults are located within the basin, along the axis of the Graben. In the area, the instrumental seismicity is low to moderate, although one major historical earthquake (Ms = 6.9 Acambay event) occurred on November 19, 1912, causing widespread damage. In the last decade, our group has focused on the neotectonic and paleoseismological study of the major faults of the Acambay graben. More than 30 trenches have been dug at 15 sites in order to interpret the paleoseismological history of 7 major faults of the graben. In addition to paleoseismological trench studies, tectonic geomorphology, subsurface geophysics and micro topographic surveys have been used to assess the rupture history. All of the studied faults have to be considered as active faults, with a minimum of 2 to 5 paleoseismic events on each fault during the last 20 ka. Each fault rupture corresponds to a vertical displacement ranging from 1 to 150 centimetres. Considering the size of the observed displacements and the length of active segments, we demonstrate that large earthquakes with magnitude higher than 7 have occurred along some of these faults. Based on paleoseismological results, we calculate a major earthquake recurrence interval ranging from 2,000 to 5,000 years over a time span (~20 ka). These recurrence values overpass the Mexican historical seismicity catalogue that incorporates no more than the last 500 years. This suggests that most of the faults of the TMVB may be active despite the lack of known historical destructive events and could be able to produce earthquakes with serious consequences in the most populated area of Mexico.
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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... more
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 on the region's population and
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Three-dimensional ground-penetrating radar GPR data are routinely acquired for diverse geologic, hydrogeologic, archeo-logical, and civil engineering purposes. Interpretations of these data are invariably based on subjective analyses of... more
Three-dimensional ground-penetrating radar GPR data are routinely acquired for diverse geologic, hydrogeologic, archeo-logical, and civil engineering purposes. Interpretations of these data are invariably based on subjective analyses of reflection pat-terns. Such analyses are heavily dependent on interpreter exper-tise and experience.Using data acquired across gravel units over-lying theAlpine Fault Zone in New Zealand, we demonstrate the utility of various geometric attributes in reducing the subjectivity of 3DGPR data analysis.We use a coherence-based technique to compute the coherency, azimuth, and dip attributes and a gray-level co-occurrence matrix GLCM method to compute the tex-ture-based energy, entropy, homogeneity, and contrast attributes. A selection of the GPR attribute volumes allows us to highlight key aspects of the fault zone and observe important features not apparent in the standard images. This selection also provides in-formation that improves our understanding of...
Surface rupture of the previously unrecognised Greendale Fault extended west-east for ~30 km across alluvial plains west of Christchurch, New Zealand, during the Mw 7.1 Darfield (Canterbury) earthquake of September 2010. Surface rupture... more
Surface rupture of the previously unrecognised Greendale Fault extended west-east for ~30 km across alluvial plains west of Christchurch, New Zealand, during the Mw 7.1 Darfield (Canterbury) earthquake of September 2010. Surface rupture displacement was predominantly dextral strike-slip, averaging ~2.5 m, with maxima of ~5 m. Vertical displacement was generally less than 0.75 m. The surface rupture deformation zone ranged in width from ~30 to 300 m, and comprised discrete shears, localised bulges and, primarily, horizontal dextral flexure. About a dozen buildings, mainly single-storey houses and farm sheds, were affected by surface rupture, but none collapsed, largely because most of the buildings were relatively flexible and resilient timber-framed structures and also because deformation was distributed over a relatively wide zone. There were, however, notable differences in the respective performances of the buildings. Houses with only lightly-reinforced concrete slab foundations ...
Research Interests: Geology and Earthquake
Lake Poerua is a small, shallow lake that abuts the scarp of the Alpine Fault on the West Coast of New Zealand’s South Island. Radiocarbon dates from drowned podocarp trees on the lake floor, a sediment core from a rangefront alluvial... more
Lake Poerua is a small, shallow lake that abuts the scarp of the Alpine Fault on the West Coast of New Zealand’s South Island. Radiocarbon dates from drowned podocarp trees on the lake floor, a sediment core from a rangefront alluvial fan, and living tree ring ages have been used to deduce the late Holocene history of the lake. Remnant drowned stumps of kahikatea ( Dacrycarpus dacrydioides) at 1.7–1.9 m water depth yield a preferred time-ofdeath age at 1766–1807 AD, while a dryland podocarp and kahikatea stumps at 2.4–2.6 m yield preferred time-of-death ages of ca. 1459–1626 AD. These age ranges are matched to, but offset from, the timings of Alpine Fault rupture events at ca. 1717 AD, and either ca. 1615 or 1430 AD. Alluvial fan detritus dated from a core into the toe of a rangefront alluvial fan, at an equivalent depth to the maximum depth of the modern lake (6.7 m), yields a calibrated age of AD 1223–1413. This age is similar to the timing of an earlier Alpine Fault rupture event...
New information on the activity of the Wellington-Hutt Valley segment of the Wellington Fault, New Zealand, has become available from geological and modelling studies undertaken in the last several years as part of the “It’s Our Fault”... more
New information on the activity of the Wellington-Hutt Valley segment of the Wellington Fault, New Zealand, has become available from geological and modelling studies undertaken in the last several years as part of the “It’s Our Fault” project. There are now revised estimates of: 1) the timing of the most recent rupture, and the previous four older ruptures; 2) the size of single-event displacements; 3) the Holocene dextral slip rate; and 4) rupture statistics of the Wellington-Wairarapa fault-pair, as deduced from synthetic seismicity modelling. The conditional probability of rupture of this segment over the next 100 years is re-evaluated in light of this new information, assuming a renewal process framework. Four recurrence-time distributions (exponential, lognormal, Weibull and Brownian passage-time) are explored. The probability estimates take account of both data and parameter uncertainties. A sensitivity analysis is conducted, entertaining different bounds and shapes of the pr...
Research Interests: Geology and Geophysics
Areas that experience permanent ground deformation in earthquakes (e.g., surface fault rupture, slope failure, and/or liquefaction) typically sustain greater damage and loss compared to areas that experience strong ground shaking alone.... more
Areas that experience permanent ground deformation in earthquakes (e.g., surface fault rupture, slope failure, and/or liquefaction) typically sustain greater damage and loss compared to areas that experience strong ground shaking alone. The 2016 Mw 7.8 Kaikōura earthquake generated ≥220 km of surface fault rupture. The amount and style of surface rupture deformation varied considerably, ranging from centimetre-scale distributed folding to metre-scale discrete rupture. About a dozen buildings – mainly residential (or residential-type) structures comprising single-storey timber-framed houses, barns and wool sheds with lightweight roofing material – were directly impacted by surface fault rupture with the severity of damage correlating with both local discrete fault displacement and local strain. However, none of these buildings collapsed. This included a house built directly atop a discrete rupture that experienced ~10 m of lateral offset. The foundation and flooring system of this st...
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The Alpine Fault in New Zealand is one of only a few active transform fault boundaries worldwide that offsets continental terrains. Although paleoseismological data suggest that large earthquakes have struck the Fault in the past, it has... more
The Alpine Fault in New Zealand is one of only a few active transform fault boundaries worldwide that offsets continental terrains. Although paleoseismological data suggest that large earthquakes have struck the Fault in the past, it has been quiescent for at least the past 200 years. We have acquired five high-resolution seismic reflection profiles across the Alpine Fault a little to the north of its intersection with the Hope Fault. Slip-rates on the Alpine Fault appear to decrease by ~50% in crossing the Hope Fault from south to north, and at our study site the faulting is distinguished by step-overs and/or multiple strands. Accordingly, the goals of our seismic investigation are to define the structure of the Alpine Fault in the top few hundred metres of the subsurface with emphasis on defining its step-over or multi-strand character at the study site. Our seismic images contain evidence for significant changes in geometry across one major fault strand and an astonishingly abrupt transition from a highly reflective region to a non-reflective region across another major strand.