Transportable Array Research Articles

Pn Tomography and Anisotropy Study of the Central United States

AbstractDetailed P wave velocity and anisotropy structure of the uppermost mantle below the central United States is presented based on a tomographic inversion of Pn traveltimes for earthquakes in the range 2 to 14°. Dense raypath coverage throughout the northern Mississippi Embayment is obtained using the Northern Embayment Lithosphere Experiment and U.S. Transportable Array data sets. A detailed analysis of the trade‐off between velocity and anisotropy variations demonstrates that both are well resolved over most of the study area. Anomalously fast Pn velocities are identified below the northern Mississippi Embayment, centered on the New Madrid seismic zone. A prominent region of low velocity coincides with the southwestern margin of the Illinois basin. Pn anisotropy displays complex patterns and differs from absolute plate motion directions and SKS splitting directions. A circular pattern of fast anisotropy directions is centered on the New Madrid seismic zone and may be related to the presence of the mafic “rift pillow.”

Morphology and Surface Properties of Roach Water Transport Arrays.

We report on morphological studies of wharf roaches, Ligia exotica, which can passively absorb and transport water through the microscopic protrusions on their legs. We systematically investigated the geometrical variables of the protrusions on each podite of legs to reveal a particularized structural complexity. For the morphological analysis, each podite was split into nine different zones by grouping the protrusions with similar shapes and organization. The protrusions are shown to possess three different types of shapes located on each specific zone of the podite. In addition, the nanoscale surface morphologies of the protrusions on the wharf roach legs were probed by using atomic force microscopy, and the surface properties of the hairy arrays were determined for identifying the localized hydrophobicity distribution. The protrusion surface possessed a nanoscale periodic patterned texture, and both the valley and ridges of a periodic pattern on the protrusion surface exhibited an identical low surface energy. We suggest that the structural morphologies and distinct hydrophobicity of the protrusions can be critical in determining the directional wettability of an entire leg and important for designing a sturdy water transport and passive water-absorbing system without external energy consumption.

The Role of Variable Slab Dip in Driving Mantle Flow at the Eastern Edge of the Alaskan Subduction Margin: Insights From Shear‐Wave Splitting

AbstractAlaska provides an ideal tectonic setting for investigating the interaction between subduction and asthenospheric flow. Within the span of a few hundred kilometers along strike, the geometry of the subducting Pacific plate varies significantly and terminates in a sharp edge. Furthermore, the region documents a transition from subduction along the Aleutian Arc to strike‐slip faulting along the Pacific Northwest. To better understand mantle interactions within this subduction zone, we conduct an SKS shear‐wave splitting analysis on passive‐source seismic data collected between 2011 and 2018 at 239 broadband seismometers, including those from the Transportable Array. Anisotropic fast directions in the east of our study area parallel the Queen Charlotte and Fairweather transform faults, suggesting that the ongoing development of lithospheric anisotropy dominates the results there. However, our observed delay times (δt = 1–1.5 s) obtained across the study region may also imply an asthenospheric contribution to the splitting pattern. Our splitting observations exhibit slab‐parallel fast directions northwest of the trench and a rotation of fast directions around the northeastern slab edge. These observations suggest the presence of toroidal asthenospheric flow around the edge of the downgoing Pacific plate. We suggest that Wrangell Volcanic Field volcanism might be caused by mantle upwelling associated with this flow. Splitting observations closer to the trench can be explained by fossil anisotropy within the downgoing Pacific‐Yakutat plate combined with entrained subslab mantle. The geometry of the slab, including its variable dip and its abrupt eastern edge, thus plays an important role in governing mantle flow beneath Alaska.

(209) Characterization of the Na+/Ca2+ Exchanger (NCS) in Human DRG Neurons

Because of the importance of intracellular Ca2+ to processes ranging from protein-interactions to cell death, the concentration of cytosolic Ca2+ ([Ca2+]c) is tightly regulated by a complex array of pumps, transporters, exchangers, and binding proteins. We have recently demonstrated that the Na+/Ca2+ exchanger (NCX), in particular NCX3, plays an important role in attenuating large-increases in [Ca2+]c in a subpopulation of putative nociceptive rat dorsal root ganglion (DRG) neurons. Interestingly, we subsequently demonstrated that inflammation-induced dysregulation of [Ca2+]c in this subpopulation of putative nociceptors was due, at least in part, to a decrease in NCX activity in the sensory neuron cell body. Given the potential importance of this exchanger to nociceptive processing as well as injury-induced changes in nociceptive processing, in the face of a growing list of differences between rodent and human sensory neurons, the purpose of the present study was to characterize NCX activity in human sensory neurons. We employed electrical field stimulation to evoke Ca2+ transients in the presence and absence of LiCl or Choline-Cl bath to block NCX activity. Interestingly, electrical field stimulation of human DRG neurons, at the same parameters used in rat, evoked a much larger Ca2+ transient in both magnitude and duration. We obtained evidence of NCX activity in the majority of neurons tested. Similar to the role of NCX in rat DRG neurons, block of NCX in human DRG neurons increased the duration, but not the magnitude of the electrically evoked Ca2+ transient. However, in contrast to the rat, there appeared to be constitutive NCX activity. Consistent with a number of recent studies, these results highlight potentially important similarities and differences between rodent and human sensory neurons, underscoring the importance of human sensory neurons as a pre-clinical screen of novel therapeutics targeting the primary afferent. Research funded by NIH T32NS073548, 1R01NS083347, and R01DK107966.

Crustal Structure in Alaska From Receiver Function Analysis

AbstractNew maps of crustal thickness and Vp/Vs in Alaska and western Canada were obtained using P receiver functions recorded at 198 stations from the USArray Transportable Array and the Alaska Regional Network. Our results indicate that topography and Moho depth are correlated as crustal thickness varies from 28 to 43 km across Alaska. A thick crust occurs under the mountains in the south and north with relatively thin crust in central Alaska. The deepest crustal root beneath the Brooks Range may have lost its buoyancy based on Airy isostasy. In addition, a buoyant upper mantle is required to support the high topography in east central Alaska. Vp/Vs is determined between 1.7 and 1.8 beneath most of Alaska except a high average of 1.9 in the south central region. We attribute this high Vp/Vs to the underplating of Yakutat and Pacific oceanic crust.

P Wave Teleseismic Traveltime Tomography of the North American Midcontinent

AbstractThe remains of the 1.1‐Ga Midcontinent Rift (MCR) lie in the middle of the tectonically stable portion of North America. Previous and ongoing studies have imaged strong heterogeneity associated with the MCR in the crust but have not imaged such within the mantle. It is unclear whether this is due to the absence of rift‐related mantle structures or these studies had insufficient resolution to image them. To address this issue, we measured 46,374 teleseismic P wave delay times from seismograms recorded by the USArray Transportable Array, Superior Province Rifting EarthScope Experiment, and surrounding permanent stations. We included these and 54,866 delay times from prior studies in our tomographic inversion. We find that high‐velocity anomalies are widespread in our study area, but there are also prominent low‐velocity anomalies. Two of these are coincident with high‐Bouguer gravity anomalies associated with the MCR in Iowa and the Minnesota/Wisconsin border at 50‐ to 150‐km depth. Extensive resolution testing shows that these anomalies could be the result of downward vertical smearing of relatively low velocities from rift‐related material that “underplated" the crust, although we cannot exclude that the subcrustal mantle lithosphere beneath the MCR is anomalously enriched, hydrated, or warm. Other anomalies occur at syntaxes of the Penokean Orogen. One with the Superior Province and Marshfield Terrane in southern Minnesota and another with the Yavapai and Mazatzal Terranes, both at 100‐ to 250‐km depth. In the midmantle, we image two linear high‐velocity anomalies, interpreted as subducted fragments of the Farallon and Kula plates.

Drought or/and Heat-Stress Effects on Seed Filling in Food Crops: Impacts on Functional Biochemistry, Seed Yields, and Nutritional Quality.

Drought (water deficits) and heat (high temperatures) stress are the prime abiotic constraints, under the current and climate change scenario in future. Any further increase in the occurrence, and extremity of these stresses, either individually or in combination, would severely reduce the crop productivity and food security, globally. Although, they obstruct productivity at all crop growth stages, the extent of damage at reproductive phase of crop growth, mainly the seed filling phase, is critical and causes considerable yield losses. Drought and heat stress substantially affect the seed yields by reducing seed size and number, eventually affecting the commercial trait ‘100 seed weight’ and seed quality. Seed filling is influenced by various metabolic processes occurring in the leaves, especially production and translocation of photoassimilates, importing precursors for biosynthesis of seed reserves, minerals and other functional constituents. These processes are highly sensitive to drought and heat, due to involvement of array of diverse enzymes and transporters, located in the leaves and seeds. We highlight here the findings in various food crops showing how their seed composition is drastically impacted at various cellular levels due to drought and heat stresses, applied separately, or in combination. The combined stresses are extremely detrimental for seed yield and its quality, and thus need more attention. Understanding the precise target sites regulating seed filling events in leaves and seeds, and how they are affected by abiotic stresses, is imperative to enhance the seed quality. It is vital to know the physiological, biochemical and genetic mechanisms, which govern the various seed filling events under stress environments, to devise strategies to improve stress tolerance. Converging modern advances in physiology, biochemistry and biotechnology, especially the “omics” technologies might provide a strong impetus to research on this aspect. Such application, along with effective agronomic management system would pave the way in developing crop genotypes/varieties with improved productivity under drought and/or heat stresses.

On the application of the fk-MUSIC method to measurement of multimode surface wave phase velocity dispersion from receiver arrays

The fk-MUSIC method, little known in earthquake seismology, is reviewed and compared with two other methods—frequency domain slant-stack and UC-diagram—for measurement of surface wave phase velocity dispersion from array seismic data. The three methods have been implemented in Python for this study and we assess their capabilities and sensitivity to data characteristics using a variety of synthetic tests. This is followed by application of the methods to data from the Transportable Array component of USArray. In terms of real data applications for regional studies, we conclude all three methods are effective only when data from very long station arrays (∼ 3 − 4 times the longest wavelength of interest, so > 2000 km for upper mantle studies) is available. Moreover, although fk-MUSIC provides high resolution, it is substantially less effective than the well established UC-diagram technique, at recovering multimode dispersion.

Heterogeneous distribution of water in the mantle transition zone inferred from wavefield imaging

The amount of water in the Earth's deep mantle is critical for the evolution of the Earth. Mineral physics studies revealed that the mantle transition zone can store several times the volume of water in an ocean. However, the actual water distribution in the transition zone remains enigmatic. We used the highest resolution images produced of scatterers in the North-American transition zone derived from teleseismic data recorded by the Earthscope Transportable Array. We find that the transition zone is filled with previously unrecognized small-scale heterogeneities that produce pervasive, negative polarity signals. Simulations demonstrated the images can be explained by low-velocity bodies shaped as distributed blobs or near vertical structures. We suggest these low-velocity bodies may be heterogeneously distributed, water-enriched subducted harzburgites produced through long-term accumulation.

Upper Mantle Seismic Structure of Alaska From Rayleigh and S Wave Tomography

AbstractMantle shear velocity (Vs) structure beneath the Transportable Array (TA) in Alaska and northwestern Canada is imaged by joint inversion of Rayleigh wave dispersion and teleseismic S wave travel times. The study connects previously unsampled parts of northern and western Alaska with portions of southern Alaska imaged with earlier seismic arrays. The new Vs tomography shows contrasting lithospheric structure in the plate interior with lower Vs shallow upper mantle indicative of thinner thermal lithosphere south of the Brooks Range and along the transform margin. Higher Vs down to ~200 km beneath the Brooks Range and northern coast is consistent with the presence of a cold stable lithospheric root that may help guide intraplate deformation to the south. In the subduction‐to‐transform transition, a potential slab fragment is imaged beneath the Wrangell volcanic field where modern subduction has slowed due to the thick buoyant crust of the Yakutat terrane.

Mapping the Alaskan Moho

Research Article| October 10, 2018 Mapping the Alaskan Moho Meghan S. Miller; Meghan S. Miller aAustralian National University, Research School of Earth Sciences, Building 142 Mills Road, Canberra, Australian Capital Territory 2601, Australia, meghan.miller@anu.edu.au Search for other works by this author on: GSW Google Scholar Louis Moresi Louis Moresi bUniversity of Melbourne, School of Earth Sciences, Parkville, Victoria 3010, Australia Search for other works by this author on: GSW Google Scholar Seismological Research Letters (2018) 89 (6): 2430–2436. https://doi.org/10.1785/0220180222 Article history first online: 10 Oct 2018 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Meghan S. Miller, Louis Moresi; Mapping the Alaskan Moho. Seismological Research Letters 2018;; 89 (6): 2430–2436. doi: https://doi.org/10.1785/0220180222 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySeismological Research Letters Search Advanced Search ABSTRACT We present a series of Moho depth maps for the Alaskan region based on P receiver function estimates using data from all available broadband instrumentation from 1999 to April 2018 including the USArray Transportable Array. The average Moho depths beneath individual broadband stations are presented first as spot measurements and then used to produce a series of interpolated smooth surfaces by an adaptive triangulation process followed by the fitting of a bicubic spline. The interpolated surfaces include a measure of confidence in the interpolation and can be used to assess and determine a preferred model. The resulting Moho depth map (single continuous surface) provides a reasonable estimate of the Earth’s outermost layer thickness beneath Alaska as constrained by receiver functions for use in applications such as tomography, regional‐scale interpretations, or simulations of seismic waves. The models are provided as a python module with examples in the form of jupyter notebooks. Our original workflow is provided to allow updates to this dataset or use with other similar datasets. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Lithospheric Structure Across the Alaskan Cordillera From the Joint Inversion of Surface Waves and Receiver Functions

AbstractThe final deployment stage of the USArray Transportable Array is nearly complete with several years of high‐quality broadband seismic data across the Northern American Cordillera already publicly available. This section of the Cordillera represents a rich history of tectonic deformation and accretion events as well numerous active tectonic processes. Many of these active tectonic processes such as uplift mechanisms or magmatic systems have been interpreted from structures imaged in regional or limited 2‐D studies. To investigate the fully 3‐D nature of the crust and uppermost mantle (<70 km), we present the results of a joint receiver function, surface wave inversion for the shear wave velocity structure across the Alaskan Cordillera. Integration of our new isotropic velocity model with existing data sets, including seismicity, gravity anomalies, and other seismic imagining methods, indicates that our velocity model is consistent with previous studies while providing unprecedented additional detail. A prominent feature in our model is a low‐velocity mantle wedge. We suggest this low‐velocity mantle wedge results from subducting slab lithosphere. The tectonic significance of this interpretation is that the velocity anomaly extends further to the east than slab seismicity does, suggesting that the downgoing slab extends further to the east, albeit aseismicly. This interpretation provides a simple explanation for the location of the active Wrangell volcanoes. We expect that our velocity model will be integrated with other mantle tomography models to further refine our understanding of this complex tectonic setting.

Using Fast Marching Eikonal Solver to Compute 3‐D Pds Traveltime for Deep Receiver‐Function Imaging

AbstractIn common‐conversion‐point stacking of receiver functions, most current studies compute 3‐D relative Pds traveltime corrections by integrating traveltime anomalies along 1‐D raypaths. This ray tracing approach is generally time‐consuming and less accurate when prominent velocity anomalies exist and effects of 3‐D raypaths become significant. In this study we introduce a new scheme that utilizes a fast‐marching method eikonal solver to improve both the efficiency and accuracy of 3‐D Pds traveltime computation. We first employ a 1‐D raytracing method and the iasp91 model to calibrate the accuracy of the new scheme and optimize the parameters of the numerical solver. We then apply the new scheme to compute a massive number of Pds traveltimes using two sets of 3‐D synthetic models, one set with a high‐velocity slab and another set with a low‐velocity plume, and compare these 3‐D traveltimes with those computed with the raypath integrating approach. We find 2.7% and 11.8% raypaths in the two slab models and 7.8% and 12.0% raypaths in the two plume models show a 3‐D traveltime difference of ≥0.5 s. We apply the proposed scheme to a subset of transportable array receiver functions that sample the transition zone beneath the Yellowstone hotspot and find that a common‐conversion‐point stack using 3‐D Pds traveltimes computed by the eikonal solver method has the best focused P660s. Finally, we illustrate that computational times can be reduced by 1 to 2 orders of magnitude with the new scheme to compute 3‐D Pds traveltimes of 20,000–200,000 receiver functions.

Seismic Imaging of the North American Midcontinent Rift Using S-to-P Receiver Functions.

North America's ~1.1‐Ga failed Midcontinent Rift (MCR) is a striking feature of gravity and magnetic anomaly maps across the continent. However, how the rift affected the underlying lithosphere is not well understood. With data from the Superior Province Rifting Earthscope Experiment and the USArray Transportable Array, we constrain three‐dimensional seismic velocity discontinuity structure in the lithosphere beneath the southwestward arm of the MCR using S‐to‐P receiver functions. We image a velocity increase with depth associated with the Moho at depths of 33–40 ± 4 km, generally deepening toward the east. The Moho amplitude decreases beneath the rift axis in Minnesota and Wisconsin, where the velocity gradient is more gradual, possibly due to crustal underplating. We see hints of a deeper velocity increase at 61 ± 4‐km depth that may be the base of underplating. Beneath the rift axis further south in Iowa, we image two distinct positive phases at 34–39 ± 4 and 62–65 ± 4 km likely related to an altered Moho and an underplated layer. We image velocity decreases with depth at depths of 90–190 ± 7 km in some locations that do not geographically correlate with the rift. These include a discontinuity at depths of 90–120 ± 7 km with a northerly dip in the south that abruptly deepens to 150–190 ± 7 km across the Spirit Lake Tectonic Zone provincial suture. The negative phases may represent a patchy, frozen‐in midlithosphere discontinuity feature that likely predates the MCR and/or be related to lithospheric thickness.

The Changing Face of the Lithosphere‐Asthenosphere Boundary: Imaging Continental Scale Patterns in Upper Mantle Structure Across the Contiguous U.S. With Sp Converted Waves

AbstractJuxtaposed terranes of highly varied tectonic history make up the contiguous U.S.: the tectonically active western U.S., the largely quiescent Archean and Proterozoic cratons of the central U.S., and the Phanerozoic orogen and rifted margin of the eastern U.S. The transitions between these regions are clearly observed with Sp converted wave images of the uppermost mantle. We use common conversion point stacked Sp waves recorded by EarthScope's Transportable Array and other permanent and temporary broadband stations to image the transition from a strong velocity decrease at the lithosphere‐asthenosphere boundary (or LAB) beneath the western U.S. to deeper, less continuous features moving east that largely lie within the lithosphere. Only sparse, localized, weak phases are seen at LAB depths beneath the cratonic interior. Instead, we observe structures within the cratonic lithosphere that are most prominent within the Archean lithosphere of the Superior Craton. The transition from west to east is clearly revealed by cluster analysis, which also shows eastern U.S. mantle velocity gradients as more similar to the western U.S. than the ancient interior, particularly beneath New England and Virginia. In the western U.S., the observed strong LAB indicates a large enough velocity gradient (an average velocity drop of 10 ± 4.5% distributed over 30 ± 15 km) to imply that melt has ponded beneath the lithosphere.

Recent Developments in the Energy Strategy of Iran in the Caspian Region

Despite the fact that the production of hydrocarbons in the Caspian Sea basin is not a priority for Iran, Tehran attaches special importance to strengthening economic cooperation with the littoral states. Iran, which was out of a regional discourse for a long time, comes up with initiatives that can shape new approaches towards the regional development in a broad array of issues, including extraction and transportation of hydrocarbon resources. For instance, recent developments have shown that the Iranian authorities clearly acknowledge that the energy factor still has a prevailing influence on both the shaping and implementation of economic and foreign priorities of the Caspian states, the economy of which remains export-oriented. As a result, Iran started to prepare the ground for the joint development of the Caspian offshore deposits and resuming oil swap operations.Therefore, the main purpose of the paper is to consider Iran’s policy toward the Caspian region highlighting Tehran’s energy strategy towards the Caspian basin and focusing on the exploration activities and prospects of development of offshore fields, as well as energy cooperation with littoral states.

Importance of KUP8 for K+ uptake in rooted plantlets of Elaeis guineensis under K+ sufficient conditions

Potassium is a major nutrient essential for plant growth and development. Acquisition of this vital element and maintenance of K+ homeostasis are complex processes, facilitated by an array of membrane transporters including carriers and channels. Key mediators of K+ uptake are the KT/KUP/HAK family of transporters. The oil palm (Elaeis guineensis), is an agriculturally important crop, but the molecular mechanisms of nutrient acquisition in this plant are poorly understood. Here we report the full sequences of three KUP transporters, EgKUP3, EgKUP8 and EgKUP11, from oil palm, obtained by a combination of database searching, PCR and 5′ and 3′ RACE techniques. Gene expression analysis of these three transporters was conducted on oil palm rooted plantlets at 7, 14, and 21 days after treatment with a range of KNO3 concentrations: 0.2 mM, 10 mM and 20 mM of in root and leaf tissues. The results indicated EgKUP8 expression is significantly upregulated in root tissues under K+ depleted conditions (0.2 mM) at 14 and 21 days. In contrast, the expression of EgKUP3 and EgKUP11 was not sensitive to changes in external K+ concentration. Functional complementation using Escherichia coli knockout strain defective in K+ uptake systems revealed that all EgKUPs complemented growth at 50 mM K+ concentration while EgKUP8 was also able to complement growth at 5 mM K+ when tested at pH 7.5. In contrast, none of the EgKUPs were able to complement growth at pH 5.5 under all external K+ concentrations tested. These observations may suggest that although EgKUP8 is less efficient at <5 mM K+ and low pH condition (pH 5.5), at least, when expressed heterologously in E. coli, the escalated gene expression observed in-planta under similar environmental condition may be indicative of a more complex cellular role of EgKUP8 in K+ uptake in plants. This piece of work provides the first insights into the molecular mechanisms of mineral uptake in the oil palm and provides a number of tools for further research in this area.

Evaluating the Experimental High-Resolution Rapid Refresh–Alaska Modeling System Using USArray Pressure Observations

Abstract The High-Resolution Rapid Refresh–Alaska (HRRR-AK) modeling system provides 3-km horizontal resolution and 0–36-h forecast guidance for weather conditions over Alaska. This study evaluated the experimental version of the HRRR-AK system available from December 2016 to June 2017, prior to its operational deployment by the National Centers for Environmental Prediction in July 2018. Surface pressure observations from 158 National Weather Service (NWS) stations assimilated during the model’s production cycle and pressure observations from 101 USArray Transportable Array (TA) stations that were not assimilated were used to evaluate 265 complete 0–36-h forecasts of the altimeter setting (surface pressure reduced to sea level). The TA network is the largest recent expansion of Alaskan weather observations and provides an independent evaluation of the model’s performance during this period. Throughout the study period, systematic differences in altimeter setting between the HRRR-AK 0-h forecasts were larger relative to the unassimilated TA observations than relative to the assimilated NWS observations. Upon removal of these initial biases from each of the subsequent 1–36-h altimeter setting forecasts, the model’s 36-h forecast root-mean-square errors at the NWS and TA locations were comparable. The model’s treatment of rapid warming and downslope winds that developed in the lee of the Alaska Range during 12–15 February is examined. The HRRR-AK 0-h forecasts were used to diagnose the synoptic and mesoscale conditions during this period. The model forecasts underestimated the abrupt increases in the temperature and intensity of the downslope winds with smaller errors as the downslope wind events evolved.

Low‐Frequency Seismic Noise Characteristics From the Analysis of Co‐Located Seismic and Pressure Data

AbstractWe analyze the characteristics of seismic noise generated by surface pressure changes, using co‐located seismic and pressure data from the USArray Transportable Array for the entire year of 2014. We compare pressure and seismic signals at frequencies of 0.01 and 0.02 Hz and model their main characteristics. At these frequencies, vertical and horizontal seismic noise can be explained by the formulas SZ = A * Sp + NZ and SH = B * Sp + NH, where SZ and SH are the power spectral densities of vertical and horizontal ground velocities (sum of two horizontal components), Sp is the power spectral density of pressure, and NZ and NH are constant terms. We first determine A and B from the high pressure range (Sp &gt; 10 Pa2/Hz) in which NZ and NH are small. From A and B, we then determine the near‐surface rigidity and pressure wave speed. This rigidity is modified from true rigidity by a factor (λ + μ)/(λ + 2 μ); this factor is about 0.7 for typical crustal rocks but approaches 1 near the Earth's surface. To estimate true rigidity, empirical formulas that relate density and seismic velocities are needed. Once A and B are determined, NZ and NH are determined. NZ and rigidity of the subsurface determine a threshold pressure in vertical data. NH is generally small but at some stations it changes seasonally and creates separate branches in plots of pressure versus seismic velocity. This may explain why seismic‐noise reduction approaches using co‐located pressure data often fail to work for horizontal data but usually work well for vertical data.

A New Automated Approach to Detecting and Locating Seismic Events Using Data from a Large Network

Research Article| June 26, 2018 A New Automated Approach to Detecting and Locating Seismic Events Using Data from a Large Network Catherine D. de Groot‐Hedlin; Catherine D. de Groot‐Hedlin aInstitute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093‐0225, chedlin@ucsd.eduhedlin@ucsd.edu Search for other works by this author on: GSW Google Scholar Michael A. H. Hedlin Michael A. H. Hedlin aInstitute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093‐0225, chedlin@ucsd.eduhedlin@ucsd.edu Search for other works by this author on: GSW Google Scholar Author and Article Information Catherine D. de Groot‐Hedlin aInstitute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093‐0225, chedlin@ucsd.eduhedlin@ucsd.edu Michael A. H. Hedlin aInstitute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093‐0225, chedlin@ucsd.eduhedlin@ucsd.edu Publisher: Seismological Society of America First Online: 26 Jun 2018 Online Issn: 1943-3573 Print Issn: 0037-1106 © Seismological Society of America Bulletin of the Seismological Society of America (2018) 108 (4): 2032–2045. https://doi.org/10.1785/0120180072 Article history First Online: 26 Jun 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Catherine D. de Groot‐Hedlin, Michael A. H. Hedlin; A New Automated Approach to Detecting and Locating Seismic Events Using Data from a Large Network. Bulletin of the Seismological Society of America 2018;; 108 (4): 2032–2045. doi: https://doi.org/10.1785/0120180072 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of the Seismological Society of America Search Advanced Search Abstract The Automated Event Location Using a Mesh of Arrays (AELUMA) method, originally developed for detection of atmospheric sources using infrasonic data, is modified here to detect and locate seismic events. A key feature of AELUMA is that it does not require a detailed velocity model to locate events. The new method was applied to vertical‐component seismic data recorded by the USArray Transportable Array to (1) test its efficacy when applied to a very large dataset, (2) test its ability to detect and accurately locate distinct event types across a geologically diverse region without analyst oversight, and (3) assess the sensitivity and accuracy of the method. Using data filtered from 1 to 8 Hz, 9996 events were detected in clusters within the central United States—with most events located near areas known for anthropogenic activity. The method was compared with three catalogs in Oklahoma—a region known for small anthropogenic events. In comparison with accurate locations from a template study, AELUMA detected all events from ML≥1.9 but none below ML 1.3. The median absolute origin time and location offset were 9.5 s and 6.0 km, respectively. Comparisons of AELUMA’s catalog in Oklahoma with two others (produced by Oklahoma Geological Survey [OGS] and the Array Network Facility) showed that AELUMA found more events than either catalog, including clusters of emergent events that were largely missed by the other methods. However, most of the smaller magnitude events detected by OGS were missed by AELUMA, mainly due to the sparser network used by AELUMA. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.