Seismic Instrumentation Research Articles

The Role of Oceanic Transform Faults in Seafloor Spreading: A Global Perspective From Seismic Anisotropy.

Mantle anisotropy beneath mid‐ocean ridges and oceanic transforms is key to our understanding of seafloor spreading and underlying dynamics of divergent plate boundaries. Observations are sparse, however, given the remoteness of the oceans and the difficulties of seismic instrumentation. To overcome this, we utilize the global distribution of seismicity along transform faults to measure shear wave splitting of over 550 direct S phases recorded at 56 carefully selected seismic stations worldwide. Applying this source‐side splitting technique allows for characterization of the upper mantle seismic anisotropy, and therefore the pattern of mantle flow, directly beneath seismically active transform faults. The majority of the results (60%) return nulls (no splitting), while the non‐null measurements display clear azimuthal dependency. This is best simply explained by anisotropy with a near vertical symmetry axis, consistent with mantle upwelling beneath oceanic transforms as suggested by numerical models. It appears therefore that the long‐term stability of seafloor spreading may be associated with widespread mantle upwelling beneath the transforms creating warm and weak faults that localize strain to the plate boundary.

Measuring Mountain River Discharge Using Seismographs Emplaced Within the Hyporheic Zone

AbstractFlow and sediment transport dynamics in fluvial systems play critical roles in shaping river morphology, in the design and use of riverine infrastructure, and in the broader management of watersheds. However, these properties are often difficult to measure comprehensively. Previous work has suggested the use of proximal seismic signals resulting from flow and bed load transport to construct more complete records of these fluvial processes. We investigate a small (184 km2; < 20 m3/s), snowmelt‐fed mountain river in the Northern Colorado Rocky Mountains during May–August 2015 to capture peak runoff with colocated measurements of discharge and seismic noise. Three‐component seismometers were placed in close proximity to the channel bank (~1 m) within the hyporheic zone (at times submerged beneath the water table). We recorded a broad spectrum of seismic signals excited by discharge, including novel, low‐frequency (0.1–2 Hz) signals observed predominantly on the horizontal components. The characteristics of these low‐frequency signals are not consistent with an elastically propagating seismic wave. We instead infer that they likely arise from the sensor tilting in response to viscoelastic deformation occurring near the channel and propose large‐scale turbulent eddies as a forcing mechanism. Calibrating horizontal seismic power with hydrograph flow rates over the course of a rainstorm for individual sensors, we demonstrate that these unique signals can be used to accurately estimate river discharge with simple regressions. This technique shows promise for augmenting seismic monitoring of rivers by enabling discharge rates to be estimated from outside the channel using easily deployed and noninvasive seismic instrumentation.

Nodal land seismic acquisition: The next generation

Within the last two years six new land seismic nodal acquisition systems have been launched, a pace unmatched even during the oil boom of the late 2000s/early 2010s. Any acquisition system that utilizes recording instrumentation that does not incorporate cables is often referred to as a nodal system. Some instruments, however, are beginning to blur what initially appears to be a clear boundary. For example, the U-Node system from Seismic Instruments utilizes a node that records data from up to 24 different channels that can then be stored locally or transmitted via Wi-Fi to a central system. The reduction in cabling, which is usually cited as the core advantage of nodal recording, is therefore limited to the backbone connecting the central recording system to the field recording units. In this paper we will concentrate on nodes that are designed to record data from a single point and are thus typically limited to six or fewer channels. Over the history of nodes there have been six major categories developed (listed roughly in the order of their introduction): 1. Delayed data – Data is stored on the node and then transmitted after each shot, or stacked series of shots, is completed. 2. Remote-controlled – data is recorded internally but recording is initiated via radio messages. 3. Remote-synchronized – data is recorded continuously but the timing signal is issued via radio. 4. Real-time data – Data is transmitted in real-time. 5. Real-time QC – Status and or quality control data is transmitted in real-time. 6. Blind – the node records data internally and does not provide status or QC information in real-time. In this article we look at how nodal systems have evolved over the last 50 years. We begin with a historical overview starting from the early 1970s finishing in 2015. We then introduce the latest nodal systems and look at the implications of their use for seismic survey acquisition logistics. Finally, we will discuss the implications of these new systems and make some suggestions about where future developments should lie.

Structure and fabric of the crust and uppermost mantle in the northern Canadian Cordillera from Rayleigh-wave tomography

The seismic structure and fabric of the lithosphere and underlying mantle beneath the northern Canadian Cordillera provides important constraints on its evolution and current tectonics; however, it is poorly characterized due to historically sparse networks of seismic instruments. We use data from past and recently deployed networks of broadband seismic stations in northwestern Canada and measure Rayleigh waves propagating between all available pairs of seismic stations using two complementary techniques: ambient noise and teleseismic two-station interferometry. The Rayleigh-wave data are processed to obtain phase velocity dispersion curves that are inverted for phase velocity maps at periods between 8 and 80 s. To first order these maps show high velocity anomalies within the Canadian Shield and low velocity anomalies within the Cordillera at all periods. At short periods (<30 s; mostly sensitive to crustal depths), we observe high velocity anomalies within the allochtonous accreted terranes, and low velocity anomalies bounded by autochtonous sedimentary rocks forming the fold-and-thrust belt. At longer periods (>30 s; mostly sensitive to uppermost mantle depths), high velocity anomalies of the Canadian Shield extend west past the Cordilleran Deformation Front and suggest the presence of cratonic lithosphere beneath the Cordillera, whereas the lowest velocities underlie the allochtonous terranes. Anisotropy within the crust and uppermost mantle exhibits fast-axis orientations aligned with the major faults and fabric of the Cordillera, and show evidence for vertical changes in anisotropy. These results provide new constraints on geodynamic models proposed to explain neotectonic deformation in this area.

Interactions between strike-slip earthquakes and the subduction interface near the Mendocino Triple Junction

The interactions between the North American, Pacific, and Gorda plates at the Mendocino Triple Junction (MTJ) create one of the most seismically active regions in North America. The earthquakes rupture all three plate boundaries but also include considerable intraplate seismicity reflecting the strong internal deformation of the Gorda plate. Understanding the stress levels that drive these ruptures and estimating the locking state of the subduction interface are especially important topics for regional earthquake hazard assessment. However owing to the lack of offshore seismic and geodetic instruments, the rupture process of only a few large earthquakes near the MTJ have been studied in detail and the locking state of the subduction interface is not well constrained. In this paper, first, we use the second moments inversion method to study the rupture process of the January 28, 2015 Mw 5.7 earthquake on the Mendocino transform fault that was unusually well recorded by both onshore and offshore strong motion instruments. We estimate the rupture dimension to be approximately 6 km by 3 km corresponding to a stress drop of ∼4 MPa for a crack model. Next we investigate the frictional state of the subduction interface by simulating the afterslip that would be expected there as a result of the stress changes from the 2015 earthquake and a 2010 Mw 6.5 intraplate earthquake within the subducted Gorda plate. We simulate afterslip scenarios for a range of depths of the downdip end of the locked zone defined as the transition to velocity strengthening friction and calculate the corresponding surface deformation expected at onshore GPS monuments. We can rule out a very shallow downdip limit owing to the lack of a detectable signal at onshore GPS stations following the 2010 earthquake. Our simulations indicate that the locking depth on the slab surface is at least 14 km, which suggests that the next M8 earthquake rupture will likely reach the coastline and strong shaking should be expected there.

The Station Information System (SIS): A Centralized Repository for Populating, Managing, and Distributing Metadata of the Advanced National Seismic System Stations

Creating, maintaining, and archiving accurate station metadata is critical for successful seismic network operations, data discovery, and research. The Station Information System (SIS) is a centralized repository of seismic station equipment inventory, instrument response, and site information of stations operated by regional seismic networks (RSNs) of the Advanced National Seismic System (ANSS; Filson and Arabasz, 2017). It has a web‐based user interface that enables the creation and manipulation of the corresponding metadata. The system can track the installation, maintenance, and removal of equipment from a site, which often results in the creation of new metadata epochs. SIS also computes the overall response, including gain, of a data channel by combining the responses of the underlying hardware components. SIS distributes this information in standard formats such as Federation of Digital Seismic Networks StationXML and dataless Standard for the Exchange of Earthquake Data. SIS can also be used to manage inventory of field equipment such as power, telemetry, or Global Positioning System antenna, as well as links to other site‐related repositories external to SIS to give the network operator the most complete view of a site and the overall network. This article summarizes the main features in SIS. We present its basic infrastructure, holdings, workflow, and how RSNs retrieve data from it. We also explain the reasoning to pursue one centralized repository and why it supports the goals of SIS and the ANSS. We demonstrate that by providing the ANSS network operator with a comprehensive site view, SIS enables the production of high‐quality metadata, a necessary prerequisite for producing high‐quality seismic data.

Empirical recurrence rates for ground motion signals on planetary surfaces

We determine the recurrence rates of ground motion events as a function of sensed velocity amplitude at several terrestrial locations, and make a first interplanetary comparison with measurements on the Moon, Mars, Venus and Titan. This empirical approach gives an intuitive order-of-magnitude guide to the observed ground motion (including both tectonic and ocean- and atmosphere-forced signals) of these locations as a guide to instrument expectations on future missions, without invoking interior models and specific sources: for example a Venera-14 observation of possible ground motion indicates a microseismic environment mid-way between noisy and quiet terrestrial locations. Quiet terrestrial regions see a peak velocity amplitude in mm/s roughly equal to 0.3*N(-0.7), where N is the number of “events” (half-hour intervals in which a given peak ground motion is exceeded) observed per year. The Apollo data show endogenous seismic signals for a given recurrence rate that are typically about 10,000 times smaller in amplitude than a quiet site on Earth, although local thermally-induced moonquakes are much more common. Viking data masked for low-wind periods appear comparable with a quiet terrestrial site, whereas a Venera observation of microseisms suggests ground motion more similar to a more active terrestrial location. Recurrence rate plots from in-situ measurements provide a context for seismic instrumentation on future planetary missions, e.g. to guide formulation of data compression schemes. While even small geophones can discriminate terrestrial activity rates, observations with guidance accelerometers are typically too insensitive to provide meaningful constraints (i.e. a non-zero number of “events”) on actual ground motion observations unless operated for very long periods.

Rapid earthquake detection through GPU-Based template matching

The template-matching algorithm (TMA) has been widely adopted for improving the reliability of earthquake detection. The TMA is based on calculating the normalized cross-correlation coefficient (NCC) between a collection of selected template waveforms and the continuous waveform recordings of seismic instruments. In realistic applications, the computational cost of the TMA is much higher than that of traditional techniques. In this study, we provide an analysis of the TMA and show how the GPU architecture provides an almost ideal environment for accelerating the TMA and NCC-based pattern recognition algorithms in general. So far, our best-performing GPU code has achieved a speedup factor of more than 800 with respect to a common sequential CPU code. We demonstrate the performance of our GPU code using seismic waveform recordings from the ML 6.6 Meinong earthquake sequence in Taiwan.

Evidence of magma activity from S-wave velocity structure of the Tengchong volcanic area

Tengchong is a young volcanic area near the Euro-Asian collision boundary in the southeastern Tibetan margin. Holocene volcanoes are mostly concentrated in the center of the Tengchong basin, where they construct a string-like volcanic cluster along the north-to-south direction. In order to study the magma activity and its relation with the volcanic distribution, we deployed a temporary earthquake observation within the Tengchong basin. The survey line is approximately 40 km long between the Heshui town in the south and the Gudong town in the north, passing through the Laoguipo, Dayingshan, Dakongshan, Xiaokongshan volcanoes and the Crater Lake. Broadband seismic instruments were installed at nine stations with an average 4 km spacing. The observation operated for a period of 14 months from May 2015 to July 2016. According to the Chinese Earthquake Bulletins, we selected 61 teleseismic events with magnitudes greater than M s 5.0 and distance ranges between 30° and 90°. They include 1 M s≥8.0 event, 9 M s≥7.0 events, 49 M s≥ 6.0 events, 2 M s≥5.0 events. Most of the events were located in the western Pacific region, however, they were very rare in west of the study area. Finally, 612 teleseismic waveforms are obtained from the recoding data at nine stations. A time-domain deconvolution technique is employed to compute receiver functions, in which the maximum entropy as the rule to determine auto-correlation and cross-correlation functions is used to calculate receiver functions. The advantage of this is to extract valid signals that are overwhelmed by background noise. The length-scale of seismic structure is sensitive to the waveform frequency, thus two Gaussian filters (1.0 and 2.5) were applied to constrain the receiver functions. The former is used to extract large-scale velocity structures and the latter to resolve detailed structures. Due to the low signal/noise ratio for receiver functions with G >2.5, they are not used in our inversion. The neighborhood algorithm (NA) was used for the receiver function inversion. This approach is a derivative-free searching method for finding models of acceptable data fit in a multi-dimensional parameter space. The objective is to find an ensemble of models that preferentially sampleregions of parameter space that exhibit a good fit to data, rather than seeking a single optimal model. A synthetic receiver function is calculated from the true model using the Thomson-Haskell matrix method. We selected 1000 minimal misfit models to calculate the average S-wave velocity model for each station. Results from nine stations show that there is an interconnected low-velocity zone beneath the Dayingshan, Dakongshan and Heikongshan volcanoes. It is 6–15 km at depth and ranges ~16 km from north to south. A small, low-velocity zone is found beneath the Crater Lake, which is situated at 9–16 km depth with a size of ≤8 km. They are considered to indicators of magma chambers beneath the volcanoes. A heat flow channel which connects two magma chambers can be recognized in the deep crust. To the south, prominent low velocities are observed beneath the Laoguipo volcano, suggesting strong magma activities at depths of 10–25 km, partly affected by the intersection of the Dayingjiang fault zone and the Tengchong volcanic fault zone. It may belong to another magma chamber within the crust also connected to the nearby Maanshan volcano. The Moho depth of the volcanic area varies between 38 and 41 km and is partially elevated beneath the Dakongshan volcano group. For some stations, the Moho appears to be a transition zone with an open channel for the heat flow into the crust from the upper mantle.

Crustal structure across the eastern North American margin from ambient noise tomography

AbstractPassive tectonic margins, like the eastern North American margin (ENAM), represent the meeting of oceanic and continental material where no active deformation is occurring. The recent ENAM Community Seismic Experiment provides an opportunity to examine the crustal structure across the ENAM owing to the simultaneous deployment of offshore and onshore seismic instrumentation. Using Rayleigh wave phase and group velocities derived from ambient noise data, we invert for shear velocity across the ENAM. We observe a region of transitional crustal thicknesses that connects the oceanic and continental crusts. Associated with the transitional crust is a localized positive gravitational anomaly. Farther east, the East Coast magnetic anomaly (ECMA) is located at the intersection of the transitional and oceanic crusts. We propose that underplating of dense magmatic material along the bottom of the transitional crust is responsible for the gravitational anomaly and that the ECMA demarks the location of initial oceanic crustal formation.

Magma reflection imaging in Krafla, Iceland, using microearthquake sources

AbstractThe details of magma plumbing beneath active volcanoes remain a major challenge in geochemistry, geophysics, and volcanic hazard evaluation. Here we apply a relatively novel variation of seismic interferometry, which we call Virtual Reflection Seismic Profiling, to produce a high‐resolution image of a known crustal magma body. The technique takes advantage of recent advances in both seismic instrumentation (dense arrays) and seismic analysis (seismic interferometry). We have applied this technique to data recently acquired at an iconic volcanic system, Krafla, which lies on the mid‐Atlantic ridge as exposed in northern Iceland. What make this particular site exceptional are encounters with rhyolitic magma in two drill holes, K‐39 and Iceland Deep Drilling Project‐1 (IDDP‐1). These known magma bodies represent a unique calibration opportunity for surface geophysical measurements of magma distribution at depth. In this study, we produced a stacked, seismic reflection section by applying common depth point processing techniques to virtual shot gathers derived from interferometry of P waves from microearthquakes generated by tectonic, magmatic, and/or geothermal activity. We observe a strong, coherent reflection on the seismic section at a travel time corresponding to the depth at which magma was encountered in the IDDP‐1 wellbore. We interpret this reflection to be from magma or magma‐related fluids. Additional coherent reflections may correspond to other components of the magma plumbing beneath Krafla. These results represent a promising new technique for structural imaging with natural sources that can be applied to a wide array of geologic and energy problems that involve natural or induced seismic clusters.

Big mantle wedge, anisotropy, slabs and earthquakes beneath the Japan Sea

The Japan Sea is a part of the western Pacific trench-arc-backarc system and has a complex bathymetry and intense seismic activities in the crust and upper mantle. Local seismic tomography revealed strong lateral heterogeneities in the crust and uppermost mantle beneath the eastern margin of the Japan Sea, which was determined using P and S wave arrival times of suboceanic earthquakes relocated precisely with sP depth phases. Ambient-noise tomography revealed a thin crust and a thin lithosphere beneath the Japan Sea and significant low-velocity (low-V) anomalies in the shallow mantle beneath the western and eastern margins of the Japan Sea. Observations with ocean-bottom seismometers and electromagnetometers revealed low-V and high-conductivity anomalies at depths of 200–300km in the big mantle wedge (BMW) above the subducting Pacific slab, and the anomalies are connected with the low-V zone in the normal mantle wedge beneath NE Japan, suggesting that both shallow and deep slab dehydrations occur and contribute to the arc and back-arc magmatism. The Pacific slab has a simple geometry beneath the Japan Sea, and earthquakes occur actively in the slab down to a depth of ∼600km beneath the NE Asian margin. Teleseismic P and S wave tomography has revealed that the Philippine Sea plate has subducted aseismically down to the mantle transition zone (MTZ, 410–660km) depths beneath the southern Japan Sea and the Tsushima Strait, and a slab window is revealed within the aseismic Philippine Sea slab. Seismic anisotropy tomography revealed a NW-SE fast-velocity direction in the BMW, which reflects corner flows induced by the fast deep subduction of the Pacific slab. Large deep earthquakes (M>7.0; depth>500km) occur frequently beneath the Japan Sea western margin, which may be related to the formation of the Changbai and Ulleung intraplate volcanoes. A metastable olivine wedge is revealed within the cold core of the Pacific slab at the MTZ depth, which may be related to the deep seismicity. However, many of these results are still preliminary, due to the lack of seismic stations in the Japan Sea. The key to resolving these critical geoscientific issues is seismic instrumentation in the Japan Sea, for which international cooperation of geoscience communities in the East Asian countries is necessary.

Characterizing global infrasonic ocean ambient noise

The ability of the International Monitoring System (IMS) global infrasound network to detect atmospheric explosions and events of interest strongly depends on station specific ambient noise which includes both incoherent wind noise and real coherent infrasonic waves. To characterize the coherent ambient noise, a broadband array processing was performed on 10 years of continuous recordings at IMS stations. Multi-year comparisons between the observed and modeled directional microbarom amplitude variations at several IMS stations using two-dimensional wave energy spectrum ocean wave products are performed to build of a reference database of infrasound oceanic sources. Microseisms are attributed the same source processes as microbaroms, involving the interaction of standing ocean waves. To further evaluate oceanic wave action models, the infrasound analysis will be supplemented with several other approaches including microseisms collected at seismic instrumentation (single stations and arrays). The expected benefits of such studies concern the use of multi-year complementary data to finely characterize coupling mechanisms at the ocean-atmosphere interface. In return, a better knowledge of the source of the ambient ocean noise opens new perspectives by providing additional integrated constraints on the dynamics of the middle atmosphere and its disturbances where data coverage is sparse.

Repeatability of Testing a Small Broadband Sensor in the Albuquerque Seismological Laboratory Underground Vault

Abstract Variability in seismic instrumentation performance plays a fundamental role in our ability to carry out experiments in observational seismology. Many such experiments rely on the assumed performance of various seismic sensors as well as on methods to isolate the sensors from nonseismic noise sources. We look at the repeatability of estimating the self‐noise, midband sensitivity, and the relative orientation by comparing three collocated Nanometrics Trillium Compact sensors. To estimate the repeatability, we conduct a total of 15 trials in which one sensor is repeatedly reinstalled, alongside two undisturbed sensors. We find that we are able to estimate the midband sensitivity with an error of no greater than 0.04% with a 99th percentile confidence, assuming a standard normal distribution. We also find that we are able to estimate mean sensor self‐noise to within ±5.6 dB with a 99th percentile confidence in the 30–100‐s‐period band. Finally, we find our relative orientation errors have a mean difference in orientation of 0.0171° from the reference, but our trials have a standard deviation of 0.78°. Electronic Supplement: Table of dates of the trials used as well as Q – Q plots for the statistics collected from the sensor tests.

Explosive processes during the 2015 eruption of Axial Seamount, as recorded by seafloor hydrophones

AbstractFollowing the installation of the Ocean Observatories Initiative cabled array, the 2015 eruption of Axial Seamount, Juan de Fuca ridge, became the first submarine eruption to be captured in real time by seafloor seismic and acoustic instruments. This eruption also marked the first instance where the entire eruption cycle of a submarine volcano, from the previous eruption in 2011 to the end of the month‐long 2015 event, was monitored continuously using autonomous ocean bottom hydrophones. Impulsive sounds associated with explosive lava‐water interactions are identified within hydrophone records during both eruptions. Explosions within the caldera are acoustically distinguishable from those occurring in association with north rift lava flows erupting in 2015. Acoustic data also record a series of broadband diffuse events, occurring in the waning phase of the eruption, and are interpreted as submarine Hawaiian explosions. This transition from gas‐poor to gas‐rich eruptive activity coincides with an increase in water temperature within the caldera and with a decrease in the rate of deflation. The last recorded diffuse events coincide with the end of the eruption, represented by the onset of inflation. All the observed explosion signals couple strongly into the water column, and only weakly into the solid Earth, demonstrating the importance of hydroacoustic observations as a complement to seismic and geodetic studies of submarine eruptions.

Offshore Rayleigh group velocity observations of the South Island, New Zealand, from ambient noise data

We thank Captain and Crew of the R/V Thomas G. Thompson (cruise TN229), the R/V Roger Revelle (cruise RR1002), and the SIO OBSIP facility for expert assistance at sea. The OBS instruments used in this field program were provided by the U.S. National Ocean Bottom Seismic Instrumentation Pool (http://www.obsip.org). MOANA seismic data are archived at the IRIS Data Management Center. The collection of ocean bottom seismic data was funded by the National Science Foundation under grants EAR-0409564, EAR-0409609, and EAR-0409835. New Zealand onshore seismic data made available by the GeoNet project, sponsored by EQC, GNS Science, and LINZ. J. Stachnik acknowledges support from the CIRES postdoctoral fellowship program.. F.-C. Lin was supported by NSF grant CyberSEES- 1442665 and the King Abdullah University of Science and Technology (KAUST) under award OCRF-2014-CRG3- 2300. We thank Martha Savage, Dan Zietlow, Justin Ball, Craig Jones, Bill Fry, and Peter Molnar for valuable comments and discussion, and John Collins for leading the MOANA OBS experiment. We thank two anonymous reviewers and Editor Mike Ritzwoller for their constructive comments.

MEMS-based seismic intensity instrument for earthquake early warning

Micro-electro-mechanical systems (MEMS)-based tri-axial seismometer can be employed to design intensity instrument and construct early warning network. Using average period τc and peak amplitude of displacement Pd methods, the estimation relationships between seismometer and magnitude can be calculated. This work outlines the algorithm and first-hand experience using low-cost MEMS-based seismometer in seismic intensity instrument. τc and Pd methods are employed to calculate magnitude estimation and STA/LTA trigger algorithm is used to identify seismic event. A set of simulated earthquake wave experiments on a horizontal vibration table are used to testify the ability of P-wave identification. The results show that the accuracy of P-wave identification and seismic intensity judgement is over 95%, which proves the usability of improving implementations for the MEMS-based seismometer in the earthquake early warning application.

MEMS-based seismic intensity instrument for earthquake early warning

Micro-electro-mechanical systems (MEMS)-based tri-axial seismometer can be employed to design intensity instrument and construct early warning network. Using average period τc and peak amplitude of displacement Pd methods, the estimation relationships between seismometer and magnitude can be calculated. This work outlines the algorithm and first-hand experience using low-cost MEMS-based seismometer in seismic intensity instrument. τc and Pd methods are employed to calculate magnitude estimation and STA/LTA trigger algorithm is used to identify seismic event. A set of simulated earthquake wave experiments on a horizontal vibration table are used to testify the ability of P-wave identification. The results show that the accuracy of P-wave identification and seismic intensity judgement is over 95%, which proves the usability of improving implementations for the MEMS-based seismometer in the earthquake early warning application.

Distributed tomography with adaptive mesh refinement in sensor networks

Existing seismic instrumentation systems do not yet have the capability to recover the physical dynamics with sufficient resolution in real time. Currently, seismologists use centralised tomography inversion algorithm, which requires manual data gathering from each station and months to generate tomography. To address these issues a distributed approach is required which can avoid data collection from large number of sensors and perform in-network imaging to real-time tomography. In this paper, we present a distributed adaptive mesh refinement AMR solution to invert seismic tomography over large dense network, which avoids centralised computation and expensive data collection. Our approach first discretises the data and filters them using adaptive mesh to make it well-conditioned. The system is implemented and evaluated using a CORE emulator and we show that the filtered well-conditioned system has lower dimension and improved convergence rate than the original system, thereby decreasing the communication overhead over the network.

A 15 year record of frontal glacier ablation rates estimated from seismic data

AbstractWe present a unique time series of continuous glacier frontal ablation rates with weekly resolution over 15 years estimated from seismic calving observations at Kronebreen, Svalbard. Using linear statistical models, we calibrate the seismic record with 7 years of satellite‐derived frontal ablation measurements. The two basic input parameters required for our models are the cumulative duration of individual seismic calving events and the incompleteness of the seismic record to correct for the effect of seismic background noise. Frontal ablation follows the seasonal glacier speedup, peaking 1–2 months after the melt season maximum. Short‐lived peaks are associated with melt and rain events. Cumulative frontal ablation of Kronebreen between 2001 and 2015 is about 4.0 km3 (3.7 Gt), with the greatest annual loss (0.45 km3) between 2013 and 2014 at the onset of the recent accelerated retreat of the glacier. Our approach provides a potential method for monitoring tidewater glaciers worldwide that have sufficiently close seismic instrumentation.