A. F. Sheehan

A. F. Sheehan
University of Colorado Boulder | CUB · Department of Geological Sciences

PhD

About

178
Publications
24,778
Reads
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5,584
Citations
Additional affiliations
August 1993 - present
University of Colorado Boulder
Position
  • Fellow
August 1993 - present
University of Colorado Boulder
Position
  • Professor (Full)
September 1985 - May 1991
Massachusetts Institute of Technology
Position
  • Research Assistant

Publications

Publications (178)
Article
We utilize active-source seismic interferometry with dense seismic arrays both offshore and onland to explore the utility of this method to create virtual sources and reveal body-wave reflections in these two different environments. We first utilize data from an ocean-bottom cable (OBC) array in the Gulf of Mexico with equal numbers of sources (160...
Article
Full-text available
Many types of slow earthquakes have been discovered at subduction zones around the world. However, the physical process of these slow earthquakes is not well understood. To monitor offshore slow earthquakes, a marine seismic and geodetic experiment was conducted at the Hikurangi subduction margin from May 2014 to June 2015. During this experiment,...
Article
Full-text available
We investigated the seismic velocity structure of the Hikurangi margin in New Zealand to uncover the physical features of the subduction zone and explore the relationships between microearthquake seismicity, seismic velocity structure, and slow slip events. Using local earthquake tomography with data collected from both temporary ocean bottom seism...
Article
Full-text available
We image seismic attenuation near the Hikurangi trench offshore New Zealand, using ocean bottom and land‐based seismometers, revealing high attenuation above a recurring shallow slow‐slip event and within the subducting Hikurangi Plateau. The Hikurangi subduction margin east of the North Island, New Zealand is the site of frequent shallow slow slip...
Article
Full-text available
Abstract An efficient and cost‐effective near‐field tsunami warning system is crucial for coastal communities. The existing tsunami forecasting system is based on offshore Deep‐Ocean Assessment and Reporting of Tsunamis and Global Navigation Satellite System (GNSS) buoys which are not affordable for many countries. A potential cost‐effective soluti...
Article
We demonstrate successful crustal imaging via teleseismic P-wave coda autocorrelation, using data recorded on a 261 station array of vertical-component high-frequency geophones in the area of the Bighorn Mountains, Wyoming, U.S.A. We autocorrelate the P-wave coda of 30 teleseismic events and use phase-weighted stacking to yield seismic profiles com...
Article
The Alaska Amphibious Community Seismic Experiment (AACSE) is a shoreline-crossing passive- and active-source seismic experiment that took place from May 2018 through August 2019 along an ∼700 km long section of the Aleutian subduction zone spanning Kodiak Island and the Alaska Peninsula. The experiment featured 105 broadband seismometers; 30 were...
Article
Full-text available
In this study, we developed a new search algorithm to find a multi-fault model of a complex earthquake using tsunami data, and applied it to the January 23, 2018 M7.9 Kodiak earthquake. Our method includes a Green’s function based time reverse imaging (GFTRI) approach to invert for sea surface displacement using tsunami waveforms, followed by inver...
Article
In September 2014, a five week long slow slip event (SSE) occurred near Gisborne at the northern Hikurangi subduction zone, New Zealand, and was recorded by offshore instruments deployed by the Hikurangi Ocean Bottom Investigation of Tremor and Slow Slip (HOBITSS) project. Up to 25 cm of slip occurred directly below the HOBITSS array. We calculate...
Article
Full-text available
Earthquakes are known to occur beneath southern Tibet at depths up to ~95 km. Whether these earthquakes occur within the lower crust thickened in the Himalayan collision or in the mantle is a matter of current debate. Here we compare vertical travel paths expressed as delay times between S and P arrivals for local events to delay times of P-to-S co...
Article
Full-text available
Slow slip events are part of a spectrum of aseismic processes that relieve tectonic stress on faults. Their spatial distribution in subduction zones has been linked to perturbations in fluid pressure within the megathrust shear zone and subducting oceanic crust. However, physical observations of temporal fluid pressure fluctuations through slow sli...
Article
Full-text available
In 2014–2015, the Hikurangi Ocean Bottom Investigation of Tremor and Slow Slip experiment deployed seafloor absolute pressure gauges and ocean bottom seismometers directly above a large slow slip event, allowing examination of the relationship between slow slip and earthquakes in detail. Hikurangi Ocean Bottom Investigation of Tremor and Slow Slip...
Article
The Alaska Amphibious Community Seismic Experiment is taking a close look at seismic activity along the Alaska Peninsula to understand earthquakes in this little-studied region.
Article
Full-text available
We present electrical resistivity models of the crust and upper mantle from two-dimensional (2-D) inversion of magnetotelluric (MT) data collected in the Rio Grande rift, New Mexico, USA. Previous geophysical studies of the lithosphere beneath the rift identified a low-velocity zone several hundred kilometers wide, suggesting that the upper mantle...
Article
Full-text available
The tsunami data assimilation method enables tsunami forecasting directly from observations, without the need of estimating tsunami sources. However, it requires a dense observation network to produce desirable results. Here we propose a modified method of tsunami data assimilation for regions with a sparse observation network. The method utilizes...
Article
Full-text available
We used data from 333 continuous Global Positioning System stations, including 26 stations installed in 2006–2007 as part of a collaborative EarthScope experiment, to investigate how deformation is distributed near the Rio Grande Rift. Our previous analysis, using data from 2006 to 2010, was consistent with a nearly uniform east-west distributed ex...
Article
Full-text available
We use tsunami waveforms recorded on deep water absolute pressure gauges (Deep-ocean Assessment and Reporting of Tsunamis), coastal tide gauges, and a temporary array of seafloor differential pressure gauges (DPG) to study the tsunami generated by the 15 July 2009 magnitude 7.8 Dusky Sound, New Zealand, earthquake. We first use tsunami waveform inv...
Conference Paper
Full-text available
Tsunami data assimilation method enables forecasting tsunami directly from observations, without the need of tsunami sources. However, it requires a dense observation network, preferably located offshore at deep-ocean. Here we propose a modified method of tsunami data assimilation without the need of a dense observation network. The method consists...
Article
Shallow slow slip events have been well documented offshore Gisborne at the northern Hikurangi subduction margin, New Zealand, and are associated with tectonic tremor downdip of the slow slip patch and increases in local microseismicity. Tremor and seismicity on the shallow subduction interface are often poorly resolved due to their distance from l...
Article
An S-wave tomogram produced from finite-frequency tomography using teleseismic travel-time measurements made on and offshore the South Island of New Zealand shows four major features: high speeds in the upper mantle under the central portion of the island, low speeds along the eastern coast, and two high-speed regions in the northwest and southwest...
Article
We present an electrical resistivity model of the crust and upper mantle from two-dimensional (2D) anisotropic inversion of magnetotelluric data collected along a 450 km transect of the Rio Grande Rift, southern Rocky Mountains, and High Plains in Colorado, USA. Our model provides a window into the modern-day lithosphere beneath the Rocky Mountain...
Article
Full-text available
The Raton Basin has the highest number of earthquakes in Colorado and New Mexico from 2008 to 2010. The rate of both wastewater injection and earthquakes in the Basin increased dramatically starting in 1999 and 2000, respectively. We compare seismicity (ML 0.0-4.3) in the Raton Basin from 2008 to 2010 with the location of modeled pore pressure incr...
Article
Full-text available
Mitigation of injection-induced seismicity in Greeley, Colorado, is based largely on proximity of wastewater disposal wells to seismicity and consists of cementation of the bottom of wells to eliminate connection between the disposal interval and crystalline basement. Brief injection rate reductions followed felt events, but injection rates returne...
Article
We have observed a large number of 5-15 Hz hydroacoustic arrivals in seafloor pressure data collected in 2009-2010 by the Marine Observations of Anisotropy Near Aoteroa (MOANA) experiment offshore the South Island of New Zealand. Preliminary manual picking revealed that a small number (<10%) of these signals appeared to originate from Antarctica (p...
Article
We developed a catalog of small magnitude (ML -0.1 to 4.7) seismicity across Colorado and New Mexico from the EarthScope USArray Transportable Array and CREST (Colorado Rocky Mountains Experiment and Seismic Transects) seismic networks from 2008-2010 to characterize active deformation in the Rio Grande Rift. We recorded over 900 earthquakes in the...
Article
We present azimuthally anisotropic Rayleigh group velocity models from 8 - 35 s both offshore and onshore of the South Island of New Zealand. We use MOANA (Marine Observations of Anisotropy Near Aotearoa) broadband ocean seismic data in combination with on land data from the New Zealand National Seismography Network (NZNSN) to investigate the seism...
Conference Paper
Full-text available
While tsunami signals were fully hidden in high-frequency recordings of the OBSPGs, we were able to clearly extract the tsunami signals by applying re-sampling, filtering, and de-convolving the DPG instrument response. In our processed OBSPG tsunami data, the tsunami arrival times were clear and the signals had periods in the range of 10-20 min whi...
Article
Full-text available
We apply a genetic algorithm (GA) to find the optimized unit sources using dispersive tsunami synthetics to estimate the tsunami source of the 2012 Haida Gwaii earthquake. The optimal number and distribution of unit sources gives the sea surface elevation similar to that from our previous slip distribution on a fault using tsunami data, but differe...
Article
We used a dense seismic network to test the P/S amplitude ratio discriminant for earthquakes and explosions at distances from 20 to 200 km in a complex tectonic setting. We used data from several hundred seismic stations in northern Wyoming to observe 22 earthquakes, 37 mining blasts, and 24 borehole shots and compared their P/S amplitude ratios. F...
Article
On 1 June 2014 (03:35 UTC), an Mw 3.2 earthquake occurred in Weld County, Colorado, a historically aseismic area of the Denver-Julesburg basin. Weld County is a prominent area of oil and gas development, including many high-rate class II wastewater injection wells. In the days following the earthquake, the University of Colorado, with support from...
Article
The range of fault slip behaviors near the trench at subduction plate boundaries is critical to know, as this is where the world’s largest, most damaging tsunamis are generated. Our knowledge of these behaviors has remained largely incomplete, partially due to the challenging nature of crustal deformation measurements at offshore plate boundaries....
Article
A P wave speed tomogram produced from teleseismic travel time measurements made on and offshore the South Island of New Zealand shows a nearly vertical zone with wave speeds that are 4.5% higher than the background average reaching to depths of approximately 450km under the northwestern region of the island. This structure is consistent with obliqu...
Article
Full-text available
Keypoints: 1. First demonstration of tsunami data assimilation method using seafloor pressure gauge array records 2. Inverted tsunami source for the 2012 Haida Gwaii earthquake consists of large fault slip and bathymetric slope displacement effect 3. Assimilation of dense tsunami data yields forecast similar to forward simulation from the source mo...
Article
We present a crust and mantle 3-D shear velocity model extending well offshore of New Zealand's South Island, imaging the lithosphere beneath the South Island as well as the Campbell and Challenger Plateaus. Our model is constructed via linearized inversion of both teleseismic (18–70 s period) and ambient noise-based (8–25 s period) Rayleigh wave d...
Article
Recent and upcoming studies of the Hikurangi margin east of New Zealand shed light on previously undetectable tectonic movements.
Conference Paper
We develop a catalog of small magnitude seismicity across Colorado and New Mexico from the Earthscope USArray Transportable Array/CREST seismic networks from 2008-2010 to characterize active deformation in the Rio Grande rift. We recorded over 800 earthquakes in the Rio Grande Rift region, not including induced earthquakes and mine blasts, and find...
Conference Paper
We present two-dimensional anisotropic inversion results from the Deep RIFT Electrical Resistivity (DRIFTER) experiment, a 450 km magnetotelluric transect of the Rio Grande Rift, southern Rocky Mountains and High Plains in central Colorado. Our model reveals a modern-day snapshot of the resistivity structure of the crust and upper mantle beneath th...
Article
We took advantage of a high-density seismic array deployed coincident with US Array to study small-magnitude seismicity patterns in northern Wyoming. We detected and located a total of 89 earthquakes ranging in magnitude from -0.5 to 2.4 during the six-month period of April to September 2010. Most events were located shallower than 25 km in the cru...
Article
Full-text available
The crustal structure of north-central Wyoming records a history of complex lithospheric evolution from Precambrian accretion to Cretaceous-Paleogene Laramide shortening. We present two active source P-wave velocity model profiles collected as part of the Bighorn Arch Seismic Experiment (BASE) in 2010. Analysis of these velocity models and single-f...
Article
Full-text available
The purpose of this article is to test the ability of the seafloor pressure sensors utilized in the Cascadia Initiative (CI) experiment (Toomey et al. , 2014) to provide useful recordings of tsunamis, and to compare the performance of the different types of seafloor pressure sensors for long‐period recordings. These tests are performed through anal...
Article
Local and regional S-wave splitting in the offshore South Island of the New Zealand plate-boundary zone provides constraints on the spatial and depth extent of the anisotropic structure with an enhanced resolution relative to land-based and SKS studies. The combined analysis of offshore and land measurements using splitting tomography suggests plat...
Article
Teleseismic body-wave imaging techniques such as receiver function analysis can be notoriously difficult to employ on ocean-bottom seismic data due largely to multiple reverberations within the water and low-velocity sediments. In lieu of suppressing this coherently scattered noise in ocean-bottom receiver functions, these site effects can be model...
Article
Basement-cored uplifts are observed globally and remain an enigmatic feature of plate tectonics due to the fact that, in many cases, they occur distant from a plate boundary. The Laramide Bighorn Arch in Wyoming is an archetypal basement-involved foreland arch and provides an excellent setting for the investigation of such structures. Previous stud...
Article
In 2010 an array of 834 single-component geophones was deployed across the Bighorn Mountain Range in northern Wyoming as part of the Bighorn Arch Seismic Experiment (BASE). The goal of this deployment was to test the capabilities of these instruments as recorders of passive-source observations in addition to active-source observations for which the...
Article
Glacial calving from polar ice sheets is an important indicator of global climate change, and knowledge of ice discharge rates is useful for predicting global sea level variability and deep ocean circulation patterns. Since calving events are difficult to observe in-situ due to the remoteness of polar regions, the remote detection of hydroacoustic...
Article
Full-text available
[1] New shear wave splitting measurements made from stations on and offshore the South Island of New Zealand show a zone of anisotropy 100 – 200 km wide. Measurements in central South Island and up to approximately 100 km offshore from the west coast yield orientations of the fast quasi-shear wave nearly parallel to relative plate motion, with incr...
Article
Full-text available
Wave interferometry is a remote sensing technique, which is increasingly employed in helioseismology, seismology, and acoustics to retrieve parameters of the propagation medium from two-point cross-correlation functions of random wave fields. Here, we apply interferometry to yearlong records of seafloor pressure at 28 locations off New Zealand's So...
Article
[1] We jointly interpret P and S wave seismic attenuation (1/Q) along with previously published seismic velocity results for the crust and uppermost mantle of eastern Nepal and the southern Tibetan Plateau. Seismic attenuation measurements can provide information complementary to seismic velocity estimates, and can help distinguish between composit...
Article
Widespread observations of tremor and slow slip in different tectonic environments (Rubinstein et al. , 2009; Schwartz and Rokosky, 2007) reveal that these newly recognized processes play fundamental roles in accommodating and marking fault motion. Understanding the relationship between fault dynamics, stable (slow) slip, and more rapid earthquake...
Article
Sub-crustal earthquakes have been observed sporadically for ˜40 years in the central South Island of New Zealand. We report on 20 events recorded between December 2008 and February 2012 near the Alpine Fault in the continental collision zone between the Australian and Pacific plates. A subset of 18 events at depths of 47-74 km occurs south of Mt. C...
Article
Full-text available
Low-velocity sedimentary basins introduce error in many standard receiver-function (RF) analysis techniques including common conversion point (Dueker and Sheehan, 1997) and crustal thickness-V-P/V-S ratio (H-kappa) stacking (Zhu and Kanamori, 2000). We describe a simple RF analysis method for obtaining accurate crustal thickness below seismic stati...
Article
Full-text available
waves (IGWs) play an important role in coupling wave processes in the ocean, ice shelves, atmosphere, and the solid Earth. Due to the paucity of experimental data, little quantitative information is available about power spectra of IGWs away from the shore. Here we use continuous, yearlong records of pressure at 28 locations on the seafloor off New...
Article
In addition to acoustic-gravity waves generated in the ocean and atmosphere by strong transient events such as earthquakes and tsunamis, there exists a certain background level of acoustic-gravity waves. Because of their large free path length and a wide spatial distribution of the wave sources, background acoustic-gravity waves form a diffuse (but...
Article
Full-text available
We analyze the characteristics of ambient noise recorded on ocean-bottom seismographs using data from the 2009-2010 MOANA (Marine Observations of Anisotropy Near Aotearoa) seismic experiment deployed west and east of South Island, New Zealand. Microseism and infragravity noise peaks are clear on data recorded on the vertical channel of the seismome...
Article
Full-text available
Online material: Complete list of earthquakes used in this study. Three-component ground-motion recordings are critical to modern seismic analysis techniques such as receiver functions and body- and surface-wave polarization studies. Modern three-component seismometers typically resolve three axes of ground motion into one vertical and two orthogo...
Article
Full-text available
We use continuous measurements of GPS sites from across the Rio Grande Rift, Great Plains, and Colorado Plateau to estimate present-day surface velocities and strain rates. Velocity gradients from five east-west profiles suggest an average of ∼1.2 nanostrains/yr east-west extensional strain rate across these three physiographic provinces. The exten...
Article
Full-text available
We demonstrate a case of using teleseisms recorded on single-channel high-frequency geophones to image upper crustal structure around the Bighorn Mountains of north-central Wyoming, USA. Our approach produces images that are analogous to those from a low frequency version of conventional active source seismic reflection profiles except that wave fi...
Poster
We present high-density crustal thickness measurements of the Bighorn Mountains of north-central Wyoming using teleseismic P-S wave receiver functions as part of the Bighorn Arch Seismic Experiment (BASE). The goal of the BASE project is to better understand how basement-involved foreland arches form, how they are connected to plate tectonics, and...
Article
Whereas basement-involved foreland arches, such as the Bighorn Arch in north-central Wyoming, are typical of Laramide-style orogenesis, the mode of arch shortening at depth remains unresolved due to lack of geophysical imaging. Current hypotheses for lithospheric geometries and kinematics across the Bighorn Arch predict distinctly different lower c...
Conference Paper
Due to its well-understood tectonic history, New Zealand is an ideal location to investigate strain at depth through seismic anisotropy studies; however, previous investigations have resulted in conflicting interpretations. Central regions of the South Island, as well as its northern end, exhibit fast axis orientations nearly parallel to the Alpine...