The Alaska Amphibious Community Seismic Experiment

2020 ◽  
Vol 91 (6) ◽  
pp. 3054-3063 ◽  
Author(s):  
Grace Barcheck ◽  
Geoffrey A. Abers ◽  
Aubreya N. Adams ◽  
Anne Bécel ◽  
John Collins ◽  
...  
Keyword(s):  
Strong Motion ◽  
Seismic Survey ◽  
Absolute Pressure ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Alaska Peninsula ◽  
Outer Rise ◽  
Kodiak Island ◽  
Active Source ◽  
Seismic Experiment

Abstract The Alaska Amphibious Community Seismic Experiment (AACSE) is a shoreline-crossing passive- and active-source seismic experiment that took place from May 2018 through August 2019 along an ∼700  km long section of the Aleutian subduction zone spanning Kodiak Island and the Alaska Peninsula. The experiment featured 105 broadband seismometers; 30 were deployed onshore, and 75 were deployed offshore in Ocean Bottom Seismometer (OBS) packages. Additional strong-motion instruments were also deployed at six onshore seismic sites. Offshore OBS stretched from the outer rise across the trench to the shelf. OBSs in shallow water (<262  m depth) were deployed with a trawl-resistant shield, and deeper OBSs were unshielded. Additionally, a number of OBS-mounted strong-motion instruments, differential and absolute pressure gauges, hydrophones, and temperature and salinity sensors were deployed. OBSs were deployed on two cruises of the R/V Sikuliaq in May and July 2018 and retrieved on two cruises aboard the R/V Sikuliaq and R/V Langseth in August–September 2019. A complementary 398-instrument nodal seismometer array was deployed on Kodiak Island for four weeks in May–June 2019, and an active-source seismic survey on the R/V Langseth was arranged in June 2019 to shoot into the AACSE broadband network and the nodes. Additional underway data from cruises include seafloor bathymetry and sub-bottom profiles, with extra data collected near the rupture zone of the 2018 Mw 7.9 offshore-Kodiak earthquake. The AACSE network was deployed simultaneously with the EarthScope Transportable Array (TA) in Alaska, effectively densifying and extending the TA offshore in the region of the Alaska Peninsula. AACSE is a community experiment, and all data were made available publicly as soon as feasible in appropriate repositories.

Soil Coupling Of a Strong Motion, Ocean Bottom Seismometer

1979 ◽  
Author(s):  
R.L. Steinmetz ◽  
P.L. Donoho ◽  
J.D. Murff ◽  
G.V. Latham
Keyword(s):  
Strong Motion ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer

scholarly journals Post-seismic response of the outer accretionary prism after the 2010 Maule earthquake, Chile

Geosphere ◽  
2019 ◽  
Vol 16 (1) ◽  
pp. 13-32 ◽  
Author(s):  
Anne M. Tréhu ◽  
Alexander de Moor ◽  
José Mieres Madrid ◽  
Miguel Sáez ◽  
C. David Chadwell ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Plate Boundary ◽  
Low Frequency ◽  
Accretionary Prism ◽  
Absolute Pressure ◽  
Ocean Bottom ◽  
Intermediate Band ◽  
Outer Rise ◽  
Maule Earthquake ◽  
Seafloor Pressure

Abstract To investigate the dynamic response of the outer accretionary prism updip from the patch of greatest slip during the 2010 Mw 8.8 Maule earthquake (Chile), 10 ocean-bottom seismometers (OBSs) were deployed from May 2012 to March 2013 in a small network with an inter-instrument spacing of 7–10 km. Nine were recovered, with four recording data from intermediate-band three-component seismometers and differential pressure gauges, and five recording data from absolute pressure gauges (APGs). All instruments were also equipped with fluid flow meters designed to detect very low rates of flow into or out of the seafloor. We present hypocenters for local earthquakes that have S-P times <17 s (i.e., within ∼125 km of the network), with a focus on events located beneath or near the network. Most of the seismicity occurred either near the boundary between the active accretionary prism and continental basement or in the outer rise seaward of the trench. For many outer-rise earthquakes, the P and S arrivals are followed by a distinctive T-phase arrival. Very few earthquakes, and none located with hypocenters deemed “reliable,” were located within the active accretionary prism or on the underlying plate boundary. Nonvolcanic tremor-like pulses and seafloor pressure transients (but no very-low-frequency earthquakes or fluid flow) were also detected. Many of the tremor observations are likely T-phases or reverberations due to soft seafloor sediments, although at least one episode may have originated within the accretionary prism south of the network. The transient seafloor pressure changes were observed simultaneously on three APGs located over the transition from the active prism to the continental basement and show polarity changes over short distances, suggesting a shallow source. Their duration of several hours to days is shorter than most geodetic transients observed using onshore GPS networks. The results demonstrate the need for densely spaced and large-aperture OBS networks equipped with APGs for understanding subduction zone behavior.

Simplifying Instrument Pools: The Next Generation Family of Smart Instrumentation.

2020 ◽  
Author(s):  
Sally Mohr ◽  
Marie Balon ◽  
Sofia Filippi ◽  
Neil Watkiss ◽  
Phil Hill
Keyword(s):  
Force Feedback ◽  
Strong Motion ◽  
Sensor Technology ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Standard Data ◽  
Long Period ◽  
Industry Standard ◽  
First Choice ◽  
Wide Range

<p>As the community further expands their scope of study, pushing into different sub-disciplines and evermore challenging environments, the need for dynamic and highly adaptable systems grows. One of the challenges for instrument pool managers is finding a system that can cater for a wide range of possible use scenarios.</p><p>This is where traditional broadband, force-feedback sensors meet their limitations: with constrained frequency responses and sensitivities, they tend to target very narrow applications offering limited flexibility. When managing a pool of instruments, this translates into increasing pressure to acquire multiple units within different instrument ranges to meet the requirements for each specific application. This in turn leads to complex pool maintenance and may require operators to use unfamiliar instruments if their first choice is being used owing to a reduced number of instruments for each application within the pool.</p><p>Güralp’s 35 years’ experience in working with major national instrument pools revealed the necessity to develop flexible, easy-to use systems that could fit a wider scope of applications. This has led to a new, highly versatile smart sensor that supports extensive user configuration and ultra-wide tilt ranges.</p><p>The new sensor has a configurable long period corner allowing for rapid deployment in a range of environments: the 1s mode ensures the sensor settles quickly for rapid response purposes, and the 120s mode is ideally suited for long period observation.</p><p>The group of products that use this technology deliver high sensor reliability, sophisticated tools for ease of instrument and data management as well as industry standard data formats. The sensors have been integrated into various instruments: the Certimus for surface and shallow burial, the Radian for deeper postholes and boreholes, and the Fortimus for strong-motion applications.  The same philosophy also brought about Aquarius, an Ocean Bottom Seismometer that utilises the same sensor technology for the benefit of OBS pools.</p><p>This family of just four instruments covers the vast majority of seismic monitoring requirements. They represent Güralp’s solution to make instrument pool management easier and more affordable.</p><p> </p><p> </p>

scholarly journals Tilt Observations at the Seafloor by Mobile Ocean Bottom Seismometers

2021 ◽  
Vol 8 ◽  
Author(s):  
Hajime Shiobara ◽  
Aki Ito ◽  
Hiroko Sugioka ◽  
Masanao Shinohara ◽  
Toshinori Sato
Keyword(s):  
Low Cost ◽  
Pressure Gauge ◽  
Source Area ◽  
Japan Trench ◽  
Absolute Pressure ◽  
Mechanical Relaxation ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Period Range ◽  
Miyagi Prefecture

We have developed a broadband ocean bottom seismometer (BBOBS) and its new generation (BBOBS-NX) with the penetrator sensor system since 1999. With them, we performed many practical observations to create a new research category of ocean bottom broadband seismology. As the next step in seafloor geophysical observation, the BBOBS and the BBOBS-NX can be a breakthrough in realizing a geodetic observation network on the seafloor. Although vertical displacement observation by the absolute pressure gauge has been widely conducted in recent years, other geodetic observations are rarely performed. A few trials to measure the seafloor tilt were performed, but those looked inadequate for practical observations. Note that the broadband sensor in our BBOBSs has a mass position signal output, which can be used to measure the tilt change. As the horizontal component noise level of the BBOBS-NX is good at a long period range, we expected it to be adequate for the tilt measurement. At the first evaluation, we performed a comparison with a water-tube tiltmeter. The result was comparable with a resolution of better than 1 µ radian. A practical observation at the south of Boso Peninsula (KAP3 site) was conducted as the in-situ study from April, 2013. In January, 2014, a slow slip event (SSE) occurred near this site. The tilt data were processed by removing steps, mechanical relaxation, and tides. The results show a clear peak started from late December 2013. Two more 2 year-long tilt observations began in 2015: one was at the KAP3 site and another was off the Miyagi Prefecture at the slope to the Japan Trench. The latter was recovered in 2017 with about 1.5 years of data, which indicate a large continuous tilt up to several tens of µ radian. This amount of tilt can be explained by a similar already estimated SSE. Mobile tilt measurement at the seafloor can be a powerful tool to study SSEs, as they can be located above the source area and also possible to build an observation array for a practical study because of its low cost and ease of deployment compared with a seafloor borehole site.

The 2018 Mw 6.8 Zakynthos, Greece, Earthquake: Dominant Strike-Slip Faulting near Subducting Slab

2020 ◽  
Vol 91 (2A) ◽  
pp. 721-732 ◽  
Author(s):  
Efthimios Sokos ◽  
František Gallovič ◽  
Christos P. Evangelidis ◽  
Anna Serpetsidaki ◽  
Vladimír Plicka ◽  
...  
Keyword(s):  
Numerical Models ◽  
Waveform Inversion ◽  
Strong Motion ◽  
Satellite System ◽  
Strike Slip ◽  
Plate Motion ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Motion Data ◽  
Global Navigation Satellite

Abstract With different styles of faulting, the eastern Ionian Sea is an ideal natural laboratory to investigate interactions between adjacent faults during strong earthquakes. The 2018 Mw 6.8 Zakynthos earthquake, well recorded by broadband and strong-motion networks, provides an opportunity to resolve such faulting complexity. Here, we focus on waveform inversion and backprojection of strong-motion data, partly checked by coseismic Global Navigation Satellite System data. We show that the region is under subhorizontal southwest–northeast compression, enabling mixed thrust faulting and strike-slip (SS) faulting. The 2018 mainshock consisted of two fault segments: a low-dip thrust, and a dominant, moderate-dip, right-lateral SS, both in the crust. Slip vectors, oriented to southwest, are consistent with plate motion. The sequence can be explained in terms of trench-orthogonal fractures in the subducting plate and reactivated faults in the upper plate. The 2018 event, and an Mw 6.6 event of 1997, occurred near three localized swarms of 2016 and 2017. Future numerical models of the slab deformation and ocean-bottom seismometer observations may illuminate possible relations among earthquakes, swarms, and fluid paths in the region.

Earthquake activity at the Kodiak continental shelf, Alaska, determined by land and ocean bottom seismograph networks

1982 ◽  
Vol 72 (1) ◽  
pp. 207-220
Author(s):  
Jeff Lawton ◽  
Cliff Frohlich ◽  
Hans Pulpan ◽  
Gary V. Latham
Keyword(s):  
Continental Shelf ◽  
Operation Time ◽  
Structural Heterogeneity ◽  
Network Data ◽  
Earthquake Activity ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Velocity Models ◽  
Kodiak Island ◽  
Shelf Region

abstract The spatial pattern of earthquakes determined by a combined land and ocean bottom seismometer (OBS) network in the Kodiak Island shelf region differs systematically from the pattern determined by a land network and from locations determined by the International Seismological Centre (ISC). As a part of a larger study of seismic risk on the continental shelf near Kodiak Island, we augmented the University of Alaska land network by deploying 11 recoverable OBS units south of Kodiak Island for 2 months in the summer of 1979. Despite a relatively short operation time and various instrument malfunctions, the combined network detected 19 locatable earthquakes in the shelf region. Because of the structural heterogeneity of this area, the earthquakes were located with a scheme which allowed different velocity models to be used for travel-time calculations of phases traveling to different stations in the network. The locations of earthquakes determined using data from both land and OBS networks were displaced about 12 km from the hypocenters of the same earthquakes determined using only land network data. For these events on the continental shelf, azimuthal control of the joint land-OBS network is excellent, and thus the joint land-OBS network locations are considerably more reliable than locations determined with the land network data alone. When the locations of the combined land-OBS network are compared to 15 yr of teleseismic locations reported by the ISC, the center of teleseismic activity appears to be about 20 to 30 km north of the center of activity determined in our study. This difference between locally determined and teleseismically determined location is similar to that observed in other studies of earthquakes and nuclear explosions in the Aleutian arc.

The 2018 Mw 6.8 Zakynthos, Greece, earthquake – strike-slip and thrust faulting in shallow subduction

2020 ◽  
Author(s):  
Efthimios Sokos ◽  
František Gallovič ◽  
Christos P. Evangelidis ◽  
Anna Serpetsidaki ◽  
Vladimír Plicka ◽  
...  
Keyword(s):  
Numerical Models ◽  
Waveform Inversion ◽  
Broad Band ◽  
Strong Motion ◽  
Aftershock Sequence ◽  
Strike Slip ◽  
Plate Motion ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Fault Interaction

<p>On October 25, 2018, at 22:54 UTC, an Mw 6.8 earthquake occurred southwest of Zakynthos island in the Ionian Sea. This is an area with different styles of faulting and the locus of strong events thus ideal for fault interaction studies. The 2018 Zakynthos earthquake was recorded by broad-band and strong-motion networks and provides an opportunity to resolve such faulting complexity. We used waveform inversion and backprojection of strong motion data, partly verified by co-seismic GNSS data, too. The aftershock sequence was relocated, and the moment tensors of the strongest events were evaluated. Stress inversion shows that the region is under sub-horizontal southwest-northeast compression, enabling mixed thrust- and strike-slip faulting. Based on detailed waveform inversion studies, we conclude that the 2018 mainshock consisted of two fault segments: a low-dip thrust, and a dominant, moderate-dip, right-lateral strike slip, both in the crust. This model explains the observed large negative CLVD component of the mainshock. Slip vectors of both ruptured segments, oriented to SW, are consistent with plate motion in the area. The sequence can be explained in terms of trench-orthogonal fractures in the subducting plate and reactivated faults in the upper plate. The 2018 event, and an Mw 6.6 event of 1997, occurred near three localized swarms of 2016 and 2017. Future numerical models of the slab deformation and ocean-bottom seismometer observations may illuminate possible relations between earthquakes, swarms and fluid paths in the region.</p>

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