Delwayne Bohnenstiehl | North Carolina State University (original) (raw)

Papers by Delwayne Bohnenstiehl

To mitigate saltwater flooding, the waterfront and downtown areas of Port Angeles, Washington wer... more To mitigate saltwater flooding, the waterfront and downtown areas of Port Angeles, Washington were built-up with up to 8 m of anthropogenic fill beginning in 1913. Shoreline modification continued into the present as this important natural deep-water harbour along the Strait of Juan de Fuca was developed for maritime industries. This and other historical activities obscured at least two historically occupied villages and burial sites of the indigenous Coast Salish Klallam people. Since these archaeological sites remain buried beneath the modern Port Angeles waterfront knowledge of the distribution of buried landforms, coastal zone processes, and estimates of site preservation and modern disturbance potential is needed for archaeological identification and preservation efforts. We created a model of the fill thickness by combining data from: (i) field observations, where the thickness of the fill could be observed directly in the landscape; (ii) topographic differences between pre-fill sounding maps and present-day LIDARdetermined elevations; and (iii) ground-penetrating radar (GPR) surveys. The GPR surveys also helped to reconstruct the now buried palaeoenvironment by identifying tidal lagoons, beach berms and stream channel features beneath the fill layer. The history of post-glacial sea-level change, here impacted by global eustasy, glacio-isostatic and tectonic factors is the first control on the development of quasi-stable coastal landforms suitable for long-term human occupation. Knowledge of past landscapes is a critical component in the development of future archaeological site catchment 'predictive' models based upon the spatial distribution and stability of landforms and resource accessibility prior to the Euro-American historic period of intensive shoreline modification. The geophysical and geomorphic identification and spatial reconstruction of buried landforms also provides needed insight into the geology of the subsurface and its control on the flow of groundwater and contaminants across the nearshore environment.

Geochemistry, Geophysics, Geosystems, 2012

During January-February 2009, an active-source seismic survey was performed over the Eastern Lau ... more During January-February 2009, an active-source seismic survey was performed over the Eastern Lau Spreading Center in the Lau Back-Arc Basin (21 S, 176 S). Acoustic signals generated by the R/V Langseth's 36-gun pneumatic source array were recorded within the deep sound channel at offsets of 29-416 km. The local ocean acoustic environment is everywhere bottom limited, with seafloor depths within the study domain ranging from $1700-2800 m. Low-frequency (4-125 Hz) sound levels are monitored using root-mean-square, energy-flux-density and zero-to-peak measurement techniques. From these field data, transmission loss is found to exceed the predictions of a geometric spherical spreading model. At similar ranges, arrival amplitudes vary by up to 20 dB and durations vary by a factor of three to six. The depth of the seafloor beneath the air gun source exhibits a positive correlation with arrival duration and a negative correlation with range-corrected amplitude, explaining up to 30% of the observed variation in both parameters. The strength of this correlation, however, varies for stations lying at different azimuths, highlighting the importance of seafloor aspect and slope in the coupling of bottom-interacting acoustic energy into the sound channel. Range-dependent ray tracing shows that shots deployed over shallower seafloor are more likely to produce sound channel trapped signals that propagate with limited bottom interaction. This results in arrivals that are more impulsive, with shorter durations and higher amplitudes. Shots deployed in deeper water typically undergo a larger number of bounces and are characterized by more emergent, longer duration and smaller amplitude arrivals.

PLoS ONE, 2021

Soundscape ecology is an emerging field in both terrestrial and aquatic ecosystems, and provides ... more Soundscape ecology is an emerging field in both terrestrial and aquatic ecosystems, and provides a powerful approach for assessing habitat quality and the ecological response of sound-producing species to natural and anthropogenic perturbations. Little is known of how underwater soundscapes respond during and after severe episodic disturbances, such as hurricanes. This study addresses the impacts of Hurricane Irma on the coral reef sounds-cape at two spur-and-groove fore-reef sites within the Florida Keys USA, using passive acoustic data collected before and during the storm at Western Dry Rocks (WDR) and before, during and after the storm at Eastern Sambo (ESB). As the storm passed, the cumulative acoustic exposure near the seabed at these sites was comparable to a small vessel operating continuously overhead for 1-2 weeks. Before the storm, sound pressure levels (SPLs) showed a distinct pattern of low frequency diel variation and increased high frequency sound during crepuscular periods. The low frequency band was partitioned in two groups representative of soniferous reef fish, whereas the high frequency band represented snapping shrimp sound production. Daily daytime patterns in low-frequency sound production largely persisted in the weeks following the hurricane. Crepuscular sound production by snapping shrimp was maintained post-hurricane with only a small shift (~1.5dB) in the level of daytime vs nighttime sound production for this high frequency band. This study suggests that on short time scales, temporal patterns in the coral reef soundscape were relatively resilient to acoustic energy exposure during the storm, as well as changes in the benthic habitat and environmental conditions resulting from hurricane damage.

Economic Anthropology, 2020

In its origins as a concept, wealth in people depended on the circulation and accumulation of rig... more In its origins as a concept, wealth in people depended on the circulation and accumulation of rights and obligations among and over the living. But if a person is a source of wealth, what happens when the person dies? Would the person be excised from the relationships upon which wealth in people depends, or might his or her wealth remain accessible to the living? To address this question, we present the case of Oberlin Cemetery in Raleigh, North Carolina. The cemetery was the core of Oberlin Village, a freedperson's African American community founded in the mid‐nineteenth century. Today, development threatens historic resources surrounding the cemetery, but a community organization founded by descendants and neighbors has emerged to preserve and promote their heritage. We are a group of anthropologists, geologists, and historians who live and work near Oberlin Village and who collaborate to help this organization achieve its goals. Here we report how our efforts to document the cemetery's history have bolstered their advocacy and validated their claims to wealth in the people buried there. Thus we show how wealth in people extends to the dead when graves and the people within them are potent sources of value for the living.

Geophysical Journal International, 2005

The seismicity of the northern Mid-Atlantic Ridge was recorded by two hydrophone networks moored ... more The seismicity of the northern Mid-Atlantic Ridge was recorded by two hydrophone networks moored in the sound fixing and ranging (SOFAR) channel, on the flanks of the Mid-Atlantic Ridge, north and south of the Azores. During its period of operation (05/2002-09/2003), the northern 'SIRENA' network, deployed between latitudes 40 • 20 N and 50 • 30 N, recorded acoustic signals generated by 809 earthquakes on the hotspot-influenced Reykjanes Ridge. This activity was distributed between five spatio-temporal event clusters, each initiated by a moderate-to-large magnitude (4.0-5.6 M) earthquake. The rate of earthquake occurrence within the initial portion of the largest sequence (which began on 2002 October 6) is described adequately by a modified Omori law aftershock model. Although this is consistent with triggering by tectonic processes, none of the Reykjanes Ridge sequences are dominated by a single large-magnitude earthquake, and they appear to be of relatively short duration (0.35-4.5 d) when compared to previously described mid-ocean ridge aftershock sequences. The occurrence of several near-equal magnitude events distributed throughout each sequence is inconsistent with the simple relaxation of mainshock-induced stresses and may reflect the involvement of magmatic or fluid processes along this deep (>2000 m) section of the Reykjanes Ridge.

Seismic activity along the East Pacific Rise (EPR) at 9-50 N was monitored by an Ocean Bottom Sei... more Seismic activity along the East Pacific Rise (EPR) at 9-50 N was monitored by an Ocean Bottom Seismometer (OBS) array continuously from October 2003 to March 2006. These data are characterized by both discrete microearthquakes and short-period tremor signals with fundamental frequency in the 5-8 Hz band. The RMS amplitude of the velocity records within this 5-8 Hz band shows

Two oceanographic expeditions were undertaken in the northeast Pacific during April and September... more Two oceanographic expeditions were undertaken in the northeast Pacific during April and September of 2008 to collect a variety of scientific data at the sites of intense earthquake swarms that occurred from 30 March to 9 April 2008. The earthquake swarms were detected by the NOAA/PMEL and US Navy SOSUS hydrophone system in the northeast Pacific. The first swarm occurred

In November 2005, our research consortium deployed an Autonomous Underwater Hydrophone (AUH) arra... more In November 2005, our research consortium deployed an Autonomous Underwater Hydrophone (AUH) array to begin long-term hydroacoustic monitoring of the waters in the Bransfield Strait and the Drake Passage. The array takes advantage of the efficient propagation of sound in the oceans to detect, locate, and analyze the distribution of small-to moderate-size earthquakes along the South Shetland Islands, Bransfield Strait, and Scotia Sea. Preliminary review indicates the hydrophones recorded hundreds of earthquakes from the seafloor spreading centers and submarine volcanoes within the Bransfield Strait, as well as events from the subduction zone off the South Shetland Islands and from throughout the Scotia Sea. Moreover, we have observed harmonic tremor produced by the movement of large icebergs, and have detected the vocalizations of several critically endangered cetacean species.

1] An array of autonomous underwater hydrophones is used to investigate regional seismicity assoc... more 1] An array of autonomous underwater hydrophones is used to investigate regional seismicity associated with the 22 January 2006 seafloor-spreading event on the northern East Pacific Rise near 9°50 0 N. Significant earthquake activity was observed beginning 3 weeks prior to the eruption, where a total of 255 earthquakes were detected within the vicinity of the 9°50 0 N area. This was followed by a series of 252 events on 22 January and a rapid decline to background seismicity levels during the subsequent 3 days. Because of their small magnitudes, accurate locations could be derived for only 20 of these events, 18 of which occurred during a 1-h period on 22 January. These earthquakes cluster near 9°45 0 N and 9°55 0 N, at the distal ends of the young lava flows identified posteruption, where the activity displays a distinct spatialtemporal pattern, alternating from the north to the south and then back to the north. This implies either rapid bilateral propagation along the rift or the near-simultaneous injection of melt vertically from the axial magma lens. Short-duration T wave risetimes are consistent with the eruption of lavas in the vicinity of 9°50 0 N on 22 January 2006. Eruptions on 12 and 15-16 January also may be inferred from the risetime data; however, the locations of these smaller-magnitude events cannot be determined accurately. Roughly 15 h after the last earthquakes were located adjacent to the eruption site, a sequence of 16 earthquakes began to the north-northeast at a distance of 25-40 km from the 9°50 0 N site. These events are located in vicinity of the Clipperton Transform and its western inside corner, an area from which the regional hydrophone network routinely detects seismicity. Coulomb stress modeling indicates that a dike intrusion spanning the known eruptive zone to the south (9°46 0 -9°56 0 N) would act to promote normal faulting or a combination of normal faulting and transform slip within this region, with stress changes on the order of 1-10 kPa.

Geological Society of America Special Papers, 2014

Observations made during geologic mapping prior to the moment magnitude, M w 5.8 2011 Virginia (U... more Observations made during geologic mapping prior to the moment magnitude, M w 5.8 2011 Virginia (USA) earthquake are important for understanding the event. Because many Paleozoic ductile faults in the Piedmont of Virginia show signs of brittle overprint, relict faults in the epicentral area represent potential seismogenic surfaces in the modern stress regime. Three major faults that reportedly dissect the earlymiddle Paleozoic bedrock in the epicentral area are reviewed here: the Shores fault of uncertain age, which has been depicted as internal to the Early Ordovician or Cambrian metaclastic Potomac terrane; the Late Ordovician Chopawamsic fault, which represents the Potomac-Chopawamsic terrane boundary; and the late Paleozoic Long Branch fault, which is internal to the Middle Ordovician Chopawamsic terrane.

Earth and Planetary Science Letters, 2014

Available online xxxx Editor: P. Shearer Keywords: tectonic geomorphology marine terrace normal f... more Available online xxxx Editor: P. Shearer Keywords: tectonic geomorphology marine terrace normal fault uplift underplating

Eos, Transactions American Geophysical Union, 2006

Encyclopedia of Ocean Sciences, 2009

OCEANS 2010 MTS/IEEE SEATTLE, 2010

Research Corporation) with CTD, turbidity, and hydrophone sensors was operated for two days in th... more Research Corporation) with CTD, turbidity, and hydrophone sensors was operated for two days in the Northeast Lau Basin. The survey was conducted near West Mata Volcano, where in November of 2008 the NOAA PMEL Vents program observed an active eruption emanating from near its summit at 1207 m-the deepest submarine activity ever to be witnessed. Our goal was to use the glider as a forensic tool to search for other nearby eruption sites with onboard sensors that detect the chemical and hydroacoustic signatures associated with the volcanic and hydrothermal plumes. The glider was launched on May 6, 2010 at 15° 8'3.60"S-174° 6'15.00"W, approximately 40 km to the west of West Mata. It flew toward West Mata and was recovered near the summit of the volcano after repeating 13 yos during a 41hour mission. Although the recordings were affected by mechanical noise from the glider's rudder, the data demonstrate that the system can detect the wide-band noises (>1 kHz) associated with submarine volcanic and intense hydrothermal activity. The glider recorded variable acoustic amplitudes based on its distance from West Mata and temporal variations in the volcano's rate of activity, and demonstrated that these geologic processes contribute to the region's high ambient noise levels.

1] We have collected 12 kHz SeaBeam bathymetry and 120 kHz DSL-120 side-scan sonar and bathymetry... more 1] We have collected 12 kHz SeaBeam bathymetry and 120 kHz DSL-120 side-scan sonar and bathymetry data to determine the tectonic and volcanic segmentation along the fastest spreading ($150 km/Myr) part of the global mid-ocean ridge system, the southern East Pacific Rise between the Easter and Juan Fernandez microplates. This area is presently reorganizing by large-scale dueling rift propagation and possible protomicroplate tectonics. Fracture patterns observed in the side-scan data define structural segmentation scales along these ridge segments. These sometimes, but not always, correlate with linear volcanic systems defining segmentation in the SeaBeam data. Some of the subsegments behave cohesively, with in-phase tectonic activity, while fundamental discontinuities occur between other subsegments. We also collected hydrothermal plume data using sensors mounted on the DSL-120 instrument package, as well as CTDO tow-yos, to determine detailed structural and volcanic controls on the hydrothermal vent pattern observed along 600 km of the Pacific-Nazca axis. Here we report the first rigorous correlation between coregistered hydrothermal plume and high-resolution marine geophysical data on similar scales and over multisegment distances. Major plume concentrations were usually found where axial inflation was relatively high and fracture density was relatively low. These correlations suggest that hydrothermal venting is most active where the apparent magmatic budget is greatest, resulting in recent eruptions that have paved over the neovolcanic zone. Areas of voluminous acoustically dark young lava flows produced from recent fissure eruptions correlate with many of the major hydrothermal vent areas. Increased crustal permeability, as gauged by increased fracture density, does not enhance hydrothermal venting in this area. Axial summit troughs and graben are rare, probably because of frequent volcanic resurfacing in this superfast spreading environment, and are not good predictors of hydrothermal activity here. Many of the hydrothermal areas are found in inflated areas near the ends of segments, suggesting that abundant magma is being supplied to these areas.

Geophysical Research Letters, 2014

ABSTRACT Submarine landslides are an important process in volcano growth yet are rarely observed ... more ABSTRACT Submarine landslides are an important process in volcano growth yet are rarely observed and poorly understood. We show that landslides occur frequently in association with the eruption of West Mata volcano in the NE Lau Basin. These events are identifiable in hydroacoustic data recorded between ~5-20 km from the volcano, and may be recognized in spectrograms by the weak and strong power at specific frequencies generated by multipathing of sound waves. The summation of direct and surface-reflected arrivals causes interference patterns in the spectrum that change with time as the landslide propagates. Observed frequencies are consistent with propagation down the volcano's north flank in an area known to have experienced mass wasting in the past. These data allow us to estimate the distance traveled by West Mata landslides and show that they travel at average speeds of ~10-25 m/s.

OCEANS 2010 MTS/IEEE SEATTLE, 2010

A vertical autonomous hydrophone (VAUH) array useful for a long-term low-frequency underwater aco... more A vertical autonomous hydrophone (VAUH) array useful for a long-term low-frequency underwater acoustic propagation study was developed at Oregon State University (OSU), North Carolina State University and the National Oceanic and Atmospheric Administration's (NOAA) Pacific Environmental Lab (PMEL). To analyze the arrival structure of the hydroacoustic signals in deep water, we needed a multichannel vertical hydrophone array with relative timing accuracy of as good as 10 ms/year where no GPS or Network Time Protocol (NTP) is available. A new scheme takes advantage of Inductive Modem Modules (IMM® from Sea-Bird Electronics) and a low-power accurate clock (QT2001® from Q-Tech Corporation). With the master unit sending an accurate 1-PPS pulse train once a day to slave instruments over a single wire inductive modem/mooring cable, it synchronizes the other slaves' clocks and keeps the timing errors among the instruments less than 10msec. As compared to the timing synchronization methods based on three-wire serial or NTP network interface, it only requires an insulated single wire mooring cable using seawater as a return. It is robust, low power and useful for longterm time synchronization of multiple instruments serially connected. As a trial, an array consisting of three vertical autonomous hydrophones (VAUH) was deployed in the Lau Basin from December 2009 to April 2010 at 21° 25'12.60"S, 176° 12'45.50"W. Each unit was fastened on a 1000-m long 5/16" jacketed cable with a 500 m of separation. All three VAUHs recorded continuously the low frequency acoustic signal at 250-Hz sampling rate and maintained a relative timing accuracy of less than 10 ms. The acoustic record shows that the entire region is active with seismicity and submarine eruptions. The results of the four-month long monitoring and comparison with other single hydrophone moorings in the area are discussed 1 .

Since August 1991 U.S. Navy hydrophones have been used by NOAA/OSU to monitor seismicity from sea... more Since August 1991 U.S. Navy hydrophones have been used by NOAA/OSU to monitor seismicity from seafloor spreading centers in the northeast Pacific Ocean. Over the last decade, more than 10,000 earthquakes have been located using the Tertiary (T-) wave of these seafloor events recorded by this hydro-acoustic monitoring system. Before a reliable analysis of the long-term behavior of northeast Pacific

To mitigate saltwater flooding, the waterfront and downtown areas of Port Angeles, Washington wer... more To mitigate saltwater flooding, the waterfront and downtown areas of Port Angeles, Washington were built-up with up to 8 m of anthropogenic fill beginning in 1913. Shoreline modification continued into the present as this important natural deep-water harbour along the Strait of Juan de Fuca was developed for maritime industries. This and other historical activities obscured at least two historically occupied villages and burial sites of the indigenous Coast Salish Klallam people. Since these archaeological sites remain buried beneath the modern Port Angeles waterfront knowledge of the distribution of buried landforms, coastal zone processes, and estimates of site preservation and modern disturbance potential is needed for archaeological identification and preservation efforts. We created a model of the fill thickness by combining data from: (i) field observations, where the thickness of the fill could be observed directly in the landscape; (ii) topographic differences between pre-fill sounding maps and present-day LIDARdetermined elevations; and (iii) ground-penetrating radar (GPR) surveys. The GPR surveys also helped to reconstruct the now buried palaeoenvironment by identifying tidal lagoons, beach berms and stream channel features beneath the fill layer. The history of post-glacial sea-level change, here impacted by global eustasy, glacio-isostatic and tectonic factors is the first control on the development of quasi-stable coastal landforms suitable for long-term human occupation. Knowledge of past landscapes is a critical component in the development of future archaeological site catchment 'predictive' models based upon the spatial distribution and stability of landforms and resource accessibility prior to the Euro-American historic period of intensive shoreline modification. The geophysical and geomorphic identification and spatial reconstruction of buried landforms also provides needed insight into the geology of the subsurface and its control on the flow of groundwater and contaminants across the nearshore environment.

Geochemistry, Geophysics, Geosystems, 2012

During January-February 2009, an active-source seismic survey was performed over the Eastern Lau ... more During January-February 2009, an active-source seismic survey was performed over the Eastern Lau Spreading Center in the Lau Back-Arc Basin (21 S, 176 S). Acoustic signals generated by the R/V Langseth's 36-gun pneumatic source array were recorded within the deep sound channel at offsets of 29-416 km. The local ocean acoustic environment is everywhere bottom limited, with seafloor depths within the study domain ranging from $1700-2800 m. Low-frequency (4-125 Hz) sound levels are monitored using root-mean-square, energy-flux-density and zero-to-peak measurement techniques. From these field data, transmission loss is found to exceed the predictions of a geometric spherical spreading model. At similar ranges, arrival amplitudes vary by up to 20 dB and durations vary by a factor of three to six. The depth of the seafloor beneath the air gun source exhibits a positive correlation with arrival duration and a negative correlation with range-corrected amplitude, explaining up to 30% of the observed variation in both parameters. The strength of this correlation, however, varies for stations lying at different azimuths, highlighting the importance of seafloor aspect and slope in the coupling of bottom-interacting acoustic energy into the sound channel. Range-dependent ray tracing shows that shots deployed over shallower seafloor are more likely to produce sound channel trapped signals that propagate with limited bottom interaction. This results in arrivals that are more impulsive, with shorter durations and higher amplitudes. Shots deployed in deeper water typically undergo a larger number of bounces and are characterized by more emergent, longer duration and smaller amplitude arrivals.

PLoS ONE, 2021

Soundscape ecology is an emerging field in both terrestrial and aquatic ecosystems, and provides ... more Soundscape ecology is an emerging field in both terrestrial and aquatic ecosystems, and provides a powerful approach for assessing habitat quality and the ecological response of sound-producing species to natural and anthropogenic perturbations. Little is known of how underwater soundscapes respond during and after severe episodic disturbances, such as hurricanes. This study addresses the impacts of Hurricane Irma on the coral reef sounds-cape at two spur-and-groove fore-reef sites within the Florida Keys USA, using passive acoustic data collected before and during the storm at Western Dry Rocks (WDR) and before, during and after the storm at Eastern Sambo (ESB). As the storm passed, the cumulative acoustic exposure near the seabed at these sites was comparable to a small vessel operating continuously overhead for 1-2 weeks. Before the storm, sound pressure levels (SPLs) showed a distinct pattern of low frequency diel variation and increased high frequency sound during crepuscular periods. The low frequency band was partitioned in two groups representative of soniferous reef fish, whereas the high frequency band represented snapping shrimp sound production. Daily daytime patterns in low-frequency sound production largely persisted in the weeks following the hurricane. Crepuscular sound production by snapping shrimp was maintained post-hurricane with only a small shift (~1.5dB) in the level of daytime vs nighttime sound production for this high frequency band. This study suggests that on short time scales, temporal patterns in the coral reef soundscape were relatively resilient to acoustic energy exposure during the storm, as well as changes in the benthic habitat and environmental conditions resulting from hurricane damage.

Economic Anthropology, 2020

In its origins as a concept, wealth in people depended on the circulation and accumulation of rig... more In its origins as a concept, wealth in people depended on the circulation and accumulation of rights and obligations among and over the living. But if a person is a source of wealth, what happens when the person dies? Would the person be excised from the relationships upon which wealth in people depends, or might his or her wealth remain accessible to the living? To address this question, we present the case of Oberlin Cemetery in Raleigh, North Carolina. The cemetery was the core of Oberlin Village, a freedperson's African American community founded in the mid‐nineteenth century. Today, development threatens historic resources surrounding the cemetery, but a community organization founded by descendants and neighbors has emerged to preserve and promote their heritage. We are a group of anthropologists, geologists, and historians who live and work near Oberlin Village and who collaborate to help this organization achieve its goals. Here we report how our efforts to document the cemetery's history have bolstered their advocacy and validated their claims to wealth in the people buried there. Thus we show how wealth in people extends to the dead when graves and the people within them are potent sources of value for the living.

Geophysical Journal International, 2005

The seismicity of the northern Mid-Atlantic Ridge was recorded by two hydrophone networks moored ... more The seismicity of the northern Mid-Atlantic Ridge was recorded by two hydrophone networks moored in the sound fixing and ranging (SOFAR) channel, on the flanks of the Mid-Atlantic Ridge, north and south of the Azores. During its period of operation (05/2002-09/2003), the northern 'SIRENA' network, deployed between latitudes 40 • 20 N and 50 • 30 N, recorded acoustic signals generated by 809 earthquakes on the hotspot-influenced Reykjanes Ridge. This activity was distributed between five spatio-temporal event clusters, each initiated by a moderate-to-large magnitude (4.0-5.6 M) earthquake. The rate of earthquake occurrence within the initial portion of the largest sequence (which began on 2002 October 6) is described adequately by a modified Omori law aftershock model. Although this is consistent with triggering by tectonic processes, none of the Reykjanes Ridge sequences are dominated by a single large-magnitude earthquake, and they appear to be of relatively short duration (0.35-4.5 d) when compared to previously described mid-ocean ridge aftershock sequences. The occurrence of several near-equal magnitude events distributed throughout each sequence is inconsistent with the simple relaxation of mainshock-induced stresses and may reflect the involvement of magmatic or fluid processes along this deep (>2000 m) section of the Reykjanes Ridge.

Seismic activity along the East Pacific Rise (EPR) at 9-50 N was monitored by an Ocean Bottom Sei... more Seismic activity along the East Pacific Rise (EPR) at 9-50 N was monitored by an Ocean Bottom Seismometer (OBS) array continuously from October 2003 to March 2006. These data are characterized by both discrete microearthquakes and short-period tremor signals with fundamental frequency in the 5-8 Hz band. The RMS amplitude of the velocity records within this 5-8 Hz band shows

Two oceanographic expeditions were undertaken in the northeast Pacific during April and September... more Two oceanographic expeditions were undertaken in the northeast Pacific during April and September of 2008 to collect a variety of scientific data at the sites of intense earthquake swarms that occurred from 30 March to 9 April 2008. The earthquake swarms were detected by the NOAA/PMEL and US Navy SOSUS hydrophone system in the northeast Pacific. The first swarm occurred

In November 2005, our research consortium deployed an Autonomous Underwater Hydrophone (AUH) arra... more In November 2005, our research consortium deployed an Autonomous Underwater Hydrophone (AUH) array to begin long-term hydroacoustic monitoring of the waters in the Bransfield Strait and the Drake Passage. The array takes advantage of the efficient propagation of sound in the oceans to detect, locate, and analyze the distribution of small-to moderate-size earthquakes along the South Shetland Islands, Bransfield Strait, and Scotia Sea. Preliminary review indicates the hydrophones recorded hundreds of earthquakes from the seafloor spreading centers and submarine volcanoes within the Bransfield Strait, as well as events from the subduction zone off the South Shetland Islands and from throughout the Scotia Sea. Moreover, we have observed harmonic tremor produced by the movement of large icebergs, and have detected the vocalizations of several critically endangered cetacean species.

1] An array of autonomous underwater hydrophones is used to investigate regional seismicity assoc... more 1] An array of autonomous underwater hydrophones is used to investigate regional seismicity associated with the 22 January 2006 seafloor-spreading event on the northern East Pacific Rise near 9°50 0 N. Significant earthquake activity was observed beginning 3 weeks prior to the eruption, where a total of 255 earthquakes were detected within the vicinity of the 9°50 0 N area. This was followed by a series of 252 events on 22 January and a rapid decline to background seismicity levels during the subsequent 3 days. Because of their small magnitudes, accurate locations could be derived for only 20 of these events, 18 of which occurred during a 1-h period on 22 January. These earthquakes cluster near 9°45 0 N and 9°55 0 N, at the distal ends of the young lava flows identified posteruption, where the activity displays a distinct spatialtemporal pattern, alternating from the north to the south and then back to the north. This implies either rapid bilateral propagation along the rift or the near-simultaneous injection of melt vertically from the axial magma lens. Short-duration T wave risetimes are consistent with the eruption of lavas in the vicinity of 9°50 0 N on 22 January 2006. Eruptions on 12 and 15-16 January also may be inferred from the risetime data; however, the locations of these smaller-magnitude events cannot be determined accurately. Roughly 15 h after the last earthquakes were located adjacent to the eruption site, a sequence of 16 earthquakes began to the north-northeast at a distance of 25-40 km from the 9°50 0 N site. These events are located in vicinity of the Clipperton Transform and its western inside corner, an area from which the regional hydrophone network routinely detects seismicity. Coulomb stress modeling indicates that a dike intrusion spanning the known eruptive zone to the south (9°46 0 -9°56 0 N) would act to promote normal faulting or a combination of normal faulting and transform slip within this region, with stress changes on the order of 1-10 kPa.

Geological Society of America Special Papers, 2014

Observations made during geologic mapping prior to the moment magnitude, M w 5.8 2011 Virginia (U... more Observations made during geologic mapping prior to the moment magnitude, M w 5.8 2011 Virginia (USA) earthquake are important for understanding the event. Because many Paleozoic ductile faults in the Piedmont of Virginia show signs of brittle overprint, relict faults in the epicentral area represent potential seismogenic surfaces in the modern stress regime. Three major faults that reportedly dissect the earlymiddle Paleozoic bedrock in the epicentral area are reviewed here: the Shores fault of uncertain age, which has been depicted as internal to the Early Ordovician or Cambrian metaclastic Potomac terrane; the Late Ordovician Chopawamsic fault, which represents the Potomac-Chopawamsic terrane boundary; and the late Paleozoic Long Branch fault, which is internal to the Middle Ordovician Chopawamsic terrane.

Earth and Planetary Science Letters, 2014

Available online xxxx Editor: P. Shearer Keywords: tectonic geomorphology marine terrace normal f... more Available online xxxx Editor: P. Shearer Keywords: tectonic geomorphology marine terrace normal fault uplift underplating

Eos, Transactions American Geophysical Union, 2006

Encyclopedia of Ocean Sciences, 2009

OCEANS 2010 MTS/IEEE SEATTLE, 2010

Research Corporation) with CTD, turbidity, and hydrophone sensors was operated for two days in th... more Research Corporation) with CTD, turbidity, and hydrophone sensors was operated for two days in the Northeast Lau Basin. The survey was conducted near West Mata Volcano, where in November of 2008 the NOAA PMEL Vents program observed an active eruption emanating from near its summit at 1207 m-the deepest submarine activity ever to be witnessed. Our goal was to use the glider as a forensic tool to search for other nearby eruption sites with onboard sensors that detect the chemical and hydroacoustic signatures associated with the volcanic and hydrothermal plumes. The glider was launched on May 6, 2010 at 15° 8'3.60"S-174° 6'15.00"W, approximately 40 km to the west of West Mata. It flew toward West Mata and was recovered near the summit of the volcano after repeating 13 yos during a 41hour mission. Although the recordings were affected by mechanical noise from the glider's rudder, the data demonstrate that the system can detect the wide-band noises (>1 kHz) associated with submarine volcanic and intense hydrothermal activity. The glider recorded variable acoustic amplitudes based on its distance from West Mata and temporal variations in the volcano's rate of activity, and demonstrated that these geologic processes contribute to the region's high ambient noise levels.

1] We have collected 12 kHz SeaBeam bathymetry and 120 kHz DSL-120 side-scan sonar and bathymetry... more 1] We have collected 12 kHz SeaBeam bathymetry and 120 kHz DSL-120 side-scan sonar and bathymetry data to determine the tectonic and volcanic segmentation along the fastest spreading ($150 km/Myr) part of the global mid-ocean ridge system, the southern East Pacific Rise between the Easter and Juan Fernandez microplates. This area is presently reorganizing by large-scale dueling rift propagation and possible protomicroplate tectonics. Fracture patterns observed in the side-scan data define structural segmentation scales along these ridge segments. These sometimes, but not always, correlate with linear volcanic systems defining segmentation in the SeaBeam data. Some of the subsegments behave cohesively, with in-phase tectonic activity, while fundamental discontinuities occur between other subsegments. We also collected hydrothermal plume data using sensors mounted on the DSL-120 instrument package, as well as CTDO tow-yos, to determine detailed structural and volcanic controls on the hydrothermal vent pattern observed along 600 km of the Pacific-Nazca axis. Here we report the first rigorous correlation between coregistered hydrothermal plume and high-resolution marine geophysical data on similar scales and over multisegment distances. Major plume concentrations were usually found where axial inflation was relatively high and fracture density was relatively low. These correlations suggest that hydrothermal venting is most active where the apparent magmatic budget is greatest, resulting in recent eruptions that have paved over the neovolcanic zone. Areas of voluminous acoustically dark young lava flows produced from recent fissure eruptions correlate with many of the major hydrothermal vent areas. Increased crustal permeability, as gauged by increased fracture density, does not enhance hydrothermal venting in this area. Axial summit troughs and graben are rare, probably because of frequent volcanic resurfacing in this superfast spreading environment, and are not good predictors of hydrothermal activity here. Many of the hydrothermal areas are found in inflated areas near the ends of segments, suggesting that abundant magma is being supplied to these areas.

Geophysical Research Letters, 2014

ABSTRACT Submarine landslides are an important process in volcano growth yet are rarely observed ... more ABSTRACT Submarine landslides are an important process in volcano growth yet are rarely observed and poorly understood. We show that landslides occur frequently in association with the eruption of West Mata volcano in the NE Lau Basin. These events are identifiable in hydroacoustic data recorded between ~5-20 km from the volcano, and may be recognized in spectrograms by the weak and strong power at specific frequencies generated by multipathing of sound waves. The summation of direct and surface-reflected arrivals causes interference patterns in the spectrum that change with time as the landslide propagates. Observed frequencies are consistent with propagation down the volcano's north flank in an area known to have experienced mass wasting in the past. These data allow us to estimate the distance traveled by West Mata landslides and show that they travel at average speeds of ~10-25 m/s.

OCEANS 2010 MTS/IEEE SEATTLE, 2010

A vertical autonomous hydrophone (VAUH) array useful for a long-term low-frequency underwater aco... more A vertical autonomous hydrophone (VAUH) array useful for a long-term low-frequency underwater acoustic propagation study was developed at Oregon State University (OSU), North Carolina State University and the National Oceanic and Atmospheric Administration's (NOAA) Pacific Environmental Lab (PMEL). To analyze the arrival structure of the hydroacoustic signals in deep water, we needed a multichannel vertical hydrophone array with relative timing accuracy of as good as 10 ms/year where no GPS or Network Time Protocol (NTP) is available. A new scheme takes advantage of Inductive Modem Modules (IMM® from Sea-Bird Electronics) and a low-power accurate clock (QT2001® from Q-Tech Corporation). With the master unit sending an accurate 1-PPS pulse train once a day to slave instruments over a single wire inductive modem/mooring cable, it synchronizes the other slaves' clocks and keeps the timing errors among the instruments less than 10msec. As compared to the timing synchronization methods based on three-wire serial or NTP network interface, it only requires an insulated single wire mooring cable using seawater as a return. It is robust, low power and useful for longterm time synchronization of multiple instruments serially connected. As a trial, an array consisting of three vertical autonomous hydrophones (VAUH) was deployed in the Lau Basin from December 2009 to April 2010 at 21° 25'12.60"S, 176° 12'45.50"W. Each unit was fastened on a 1000-m long 5/16" jacketed cable with a 500 m of separation. All three VAUHs recorded continuously the low frequency acoustic signal at 250-Hz sampling rate and maintained a relative timing accuracy of less than 10 ms. The acoustic record shows that the entire region is active with seismicity and submarine eruptions. The results of the four-month long monitoring and comparison with other single hydrophone moorings in the area are discussed 1 .

Since August 1991 U.S. Navy hydrophones have been used by NOAA/OSU to monitor seismicity from sea... more Since August 1991 U.S. Navy hydrophones have been used by NOAA/OSU to monitor seismicity from seafloor spreading centers in the northeast Pacific Ocean. Over the last decade, more than 10,000 earthquakes have been located using the Tertiary (T-) wave of these seafloor events recorded by this hydro-acoustic monitoring system. Before a reliable analysis of the long-term behavior of northeast Pacific