Millimeter-level precision in a seafloor geodesy experiment at the Discovery transform fault, East Pacific Rise

Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 14 (2013): 4392–4402, doi:10.1002/ggge.20225.Direct-path acoustic ranging is a promising seafloor geodetic technique for continuous high-resolution monitoring of geodynamical process such as fault slip and magma intrusion. Here we report on a yearlong acoustic ranging experiment conducted across the discovery transform fault at ∼4°S on the East Pacific Rise. The ranging instruments utilized a novel acoustic signal designed to enhance precision. We find that, after correcting for variations in sound speed at the path end-points, the ranging measurements have a precision of ∼1 mm over baselines approaching 1 km in length. The primary difficulty in this particular experiment was with the physical stability of the benchmarks, which were deployed free fall from a ship. Despite the stability issues, it appears that the portion of the transform fault that the array covered was locked during the year of our survey. The primary obstacle to continuous, high sample rate, high-precision geodetic monitoring of oceanic ridges and transform faults is now limited to the construction of geodetic monuments that are well anchored into bedrock.This research was funded by the National Science Foundation OCE division under award 0351143.2014-04-0

ARAS: an automated radioactivity aliquoting system for dispensing solutions containing positron-emitting radioisotopes.

BackgroundAutomated protocols for measuring and dispensing solutions containing radioisotopes are essential not only for providing a safe environment for radiation workers but also to ensure accuracy of dispensed radioactivity and an efficient workflow. For this purpose, we have designed ARAS, an automated radioactivity aliquoting system for dispensing solutions containing positron-emitting radioisotopes with particular focus on fluorine-18 ((18)F).MethodsThe key to the system is the combination of a radiation detector measuring radioactivity concentration, in line with a peristaltic pump dispensing known volumes.ResultsThe combined system demonstrates volume variation to be within 5 % for dispensing volumes of 20 μL or greater. When considering volumes of 20 μL or greater, the delivered radioactivity is in agreement with the requested amount as measured independently with a dose calibrator to within 2 % on average.ConclusionsThe integration of the detector and pump in an in-line system leads to a flexible and compact approach that can accurately dispense solutions containing radioactivity concentrations ranging from the high values typical of [(18)F]fluoride directly produced from a cyclotron (~0.1-1 mCi μL(-1)) to the low values typical of batches of [(18)F]fluoride-labeled radiotracers intended for preclinical mouse scans (~1-10 μCi μL(-1))

Dynamic triggering and earthquake swarms on East Pacific Rise transform faults

Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 44 (2017): 702-710, doi:10.1002/2016GL070857.While dynamic earthquake triggering has been reported in several continental settings, offshore observations are rare. Oceanic transform faults share properties with continental geothermal areas known for dynamic triggering: high geothermal gradients, high seismicity rates, and frequent swarms. We study dynamic triggering along the East Pacific Rise by analyzing 1 year of seismicity recorded by Ocean Bottom Seismographs. By comparing the response to teleseismic waves from global earthquakes, we find triggering to be most sensitive to changes in normal stress and to preferentially occur above 0.25 kPa. The clearest example of triggering occurs on the Quebrada and Gofar faults after the Mw8.0 Wenchuan earthquake. On Gofar, triggered seismicity occurs between the rupture areas of large earthquakes, within a zone characterized by aseismic slip, abundant microseismicity, frequent swarms, and low Vp. We infer that lithological properties inhibiting rupture propagation, such as high porosity and fluid content, also favor dynamic triggering.WHOI SSF program; GeoSim Career Support fellowship; USGS Grant Number: G14AP000582017-07-1

The political economy of growing a rural university in the USA using online education: An examination of incentives for educational imperialism and academic capitalism

Rural colleges and universities in the USA struggle to recruit new students as their geographic region is depopulating and cost to attend classes on campus are increasing. Online education using the Internet is rapidly expanding as an effective growth strategy to reach new groups of students. In this paper we take the position that online education is a form of cultural imperialism and academic capitalism where curriculum developers and professors are motivated to enroll new students in order to maintain the credibility and strength of their programmes and host institutions. We argue that it is not our intent to be educational imperialists or capitalists. Rather these are unintended consequences of our actions. This argument is supported by political economy theory in that we are marketing a technical rational form of online education without awareness of its long‐term cultural, economic, or political ramifications. Even though we pride ourselves on developing a high quality programme that in our eyes meet the needs of our students, understanding the political economy of online education is essential if our programme that has access to the global market is to go beyond the individual needs of students and address social, cultural and political needs. We conclude that one way out of this malaise is to understand our role as instructors and course designers as a first step toward understanding the intended and unintended consequences of online education

Summary Report for the 1998-1999 STATEMAP Project: Geological Mapping to Support Improved Data-Base Development and Understanding of Critical Aquifers of Texas

This Texas STATEMAP project focuses on geologic mapping in areas where enhanced geological information can significantly impact development, land use, public education, environmental protection, and the economy. For the 1998-1999 work year, the project was divided into three subprojects. Subproject 1 addressed the third and final year of mapping in several karst aquifer areas experiencing rapid urban growth along the Edwards aquifer and recharge zone. Three map areas comprised subproject 1: West San Antonio, Austin-Georgetown, and Del Rio (Fig. 1). These areas encompass some of the fastest-growing urban regions in Texas, with development further spurred by NAFTA due to the region's proximity to major transportation routes from Mexico. A portion of the Edwards aquifer serves as the sole-source aquifer for San Antonio. Geologic maps of subproject 1 areas offer essential information for water and land resource management and construction practices. Subproject 2 involved digitally compiling existing geologic maps, originally at a scale of 1:24,000, of the West Hueco Bolson-El Paso region, which were developed for previous STATEMAP projects (Fig. 2; Table 1). The contractual outcome is a color geologic map (digital dataset) at a scale of 1:100,000, covering the West Hueco Bolson-El Paso region in Texas. This digital map holds significance as it serves as a robust geologic foundation and vital dataset for a portion of the Texas-Mexico border area experiencing rapid urban expansion, declining water resources, and environmental pressures due to development. Moreover, the mapped area includes extensive public access lands (such as Franklin Mountains and Hueco Tanks State Parks), whose management stands to benefit from the availability of digital geologic data for planning, development, and enhancing public awareness of geological processes and history.Bureau of Economic Geolog

Spatial and temporal variations in earthquake stress drop on Gofar Transform Fault, East Pacific Rise : implications for fault strength

Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 123 (2018): 7722-7740, doi:10.1029/2018JB015942.On Gofar Transform Fault on the East Pacific Rise, the largest earthquakes (6.0 ≤ MW ≤ 6.2) have repeatedly ruptured the same portion of the fault, while intervening fault segments host swarms of microearthquakes. These long‐term patterns in earthquake occurrence suggest that heterogeneous fault zone properties control earthquake behavior. Using waveforms from ocean bottom seismometers that recorded seismicity before and after an anticipated 2008 MW 6.0 mainshock, we investigate the role that differences in material properties have on earthquake rupture at Gofar. We determine stress drop for 138 earthquakes (2.3 ≤ MW ≤ 4.0) that occurred within and between the rupture areas of large earthquakes. Stress drops are calculated from corner frequencies derived using an empirical Green's function spectral ratio method, and seismic moments are obtained by fitting the omega‐square source model to the low frequency amplitude of the displacement spectrum. Our analysis yields stress drops from 0.04 to 3.2 MPa with statistically significant spatial variation, including ~2 times higher average stress drop in fault segments where large earthquakes also occur compared to fault segments that host earthquake swarms. We find an inverse correlation between stress drop and P wave velocity reduction, which we interpret as the effect of fault zone damage on the ability of the fault to store strain energy that leads to our spatial variations in stress drop. Additionally, we observe lower stress drops following the MW 6.0 mainshock, consistent with increased damage and decreased fault strength after a large earthquake.W. M. Keck Foundation; National Science Foundation Division of Ocean Sciences (OCE) Grant Number: 13525652019-03-0

Aerial Surveys of the Ocean and Atmosphere off Central California

The long-term goal is to enhance our understanding of airsea interaction in the littoral zone by means of applying simple dynamical theories to high-quality observations obtained in the field. The Monterey Bay serves as our natural laboratory for these purposes. The grant is one of a continuing series of programs to study the bay funded by the National Ocean Partnership Program NOPP and the ONR Naval Ocean Modeling and Prediction NOMP Program.Grant #s: N0001403WR20002, N0001403WR20006, N0001403WR2020

A lack of dynamic triggering of slow slip and tremor indicates that the shallow Cascadia megathrust offshore Vancouver Island is likely locked

Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 45 (2018): 11,095-11,103, doi:10.1029/2018GL079519.Great subduction zone earthquakes vary considerably in the updip extent of megathrust rupture. It is unclear if this diversity reflects variations in interseismic strain accumulation owing to the limited number of subduction zones with seafloor monitoring. We use a borehole seismic‐geodetic observatory installed at the updip end of the Cascadia fault offshore Vancouver Island to show that the megathrust there does not appear to slip in triggered tremor or slow‐slip events when subjected to moderate dynamic stress transients. Borehole tilt and seismic data from recent teleseismic M7.6–8.1 earthquakes demonstrate a lack of triggered slow slip above the Mw 4.0 level and an absence of triggered tremor despite shear‐stress transients of 1–10 kPa that were sufficient to trigger tremor on the downdip end of the interface. Our observations are most consistent with a model in which the Cascadia fault offshore Vancouver Island is locked all the way to the trench.NSF Grant Numbers: OCE‐1259243, OCE‐1259718; W. M. Keck Foundation2019-04-2

Observations of seismicity and ground motion in the Northeast U.S. Atlantic Margin from ocean‐bottom seismometer data

Author Posting. © Seismological Society of America, 2016. This article is posted here by permission of Seismological Society of America for personal use, not for redistribution. The definitive version was published in Seismological Research Letters 88 (2017): 23-31, doi:10.1785/0220160079.Earthquake data from two short‐period ocean‐bottom seismometer (OBS) networks deployed for over a year on the continental slope off New York and southern New England were used to evaluate seismicity and ground motions along the continental margin. Our OBS networks located only one earthquake of Mc∼1.5 near the shelf edge during six months of recording, suggesting that seismic activity (MLg>3.0) of the margin as far as 150–200 km offshore is probably successfully monitored by land stations without the need for OBS deployments. The spectral acceleration from two local earthquakes recorded by the OBS was found to be generally similar to the acceleration from these earthquakes recorded at several seismic stations on land and to hybrid empirical acceleration relationships for eastern North America. Therefore, the seismic attenuation used for eastern North America can be extended in this region at least to the continental slope. However, additional offshore studies are needed to verify these preliminary conclusions.This project was partially funded by the Nuclear Regulatory Commission under NRC Job Number V6166.2017-11-0

A long-term geothermal observatory across subseafloor gas hydrates, IODP Hole U1364A, Cascadia accretionary prism

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in WHOI Becker, K., Davis, E. E., Heesemann, M., Collins, J. A., & McGuire, J. J. A long-term geothermal observatory across subseafloor gas hydrates, IODP Hole U1364A, Cascadia accretionary prism. Frontiers in Earth Science, 8, (2020): 568566, https://doi.org/10.3389/feart.2020.568566We report 4 years of temperature profiles collected from May 2014 to May 2018 in Integrated Ocean Drilling Program Hole U1364A in the frontal accretionary prism of the Cascadia subduction zone. The temperature data extend to depths of nearly 300 m below seafloor (mbsf), spanning the gas hydrate stability zone at the location and a clear bottom-simulating reflector (BSR) at ∼230 mbsf. When the hole was drilled in 2010, a pressure-monitoring Advanced CORK (ACORK) observatory was installed, sealed at the bottom by a bridge plug and cement below 302 mbsf. In May 2014, a temperature profile was collected by lowering a probe down the hole from the ROV ROPOS. From July 2016 through May 2018, temperature data were collected during a nearly two-year deployment of a 24-thermistor cable installed to 268 m below seafloor (mbsf). The cable and a seismic-tilt instrument package also deployed in 2016 were connected to the Ocean Networks Canada (ONC) NEPTUNE cabled observatory in June of 2017, after which the thermistor temperatures were logged by Ocean Networks Canada at one-minute intervals until failure of the main ethernet switch in the integrated seafloor control unit in May 2018. The thermistor array had been designed with concentrated vertical spacing around the bottom-simulating reflector and two pressure-monitoring screens at 203 and 244 mbsf, with wider thermistor spacing elsewhere to document the geothermal state up to seafloor. The 4 years of data show a generally linear temperature gradient of 0.055°C/m consistent with a heat flux of 61–64 mW/m2. The data show no indications of thermal transients. A slight departure from a linear gradient provides an approximate limit of ∼10−10 m/s for any possible slow upward advection of pore fluids. In-situ temperatures are ∼15.8°C at the BSR position, consistent with methane hydrate stability at that depth and pressure.KB was supported by NSF grant OCE-1259718 for construction and deployment of the thermistor cable in the hole. Construction of the seismic-strain-tilt instrumentation was supported by a Keck Foundation grant to WHOI, and deployment and recovery of the integrated sensor string was supported by NSF grant OCE-1259243 to JM and JC. Support for the pressure-monitoring instrumentation and 2014 CTD profile was provided by the Geological Survey of Canada and Ocean Networks Canada