scholarly journals The TsuJal Amphibious Seismic Network: A Passive-Source Seismic Experiment in Western Mexico

2021 ◽  
Vol 9 ◽  
Author(s):  
Francisco Javier Núñez-Cornú ◽  
Diego Córdoba Barba ◽  
William Bandy ◽  
Juan José Dañobeitia ◽  
José Edgar Alarcón Salazar ◽  
...  
Keyword(s):  
Contact Region ◽  
Central Zone ◽  
Seismic Network ◽  
Spreading Ridge ◽  
Ocean Bottom ◽  
Transform Fault ◽  
Seismicity Rate ◽  
Seismic Experiment ◽  
Ocean Bottom Seismometers ◽  
Earthquake Distribution

The geodynamic complexity in the western Mexican margin is controlled by the multiple interactions between the Rivera, Pacific, Cocos, and North American plates, as evidenced by a high seismicity rate, most of whose hypocenters are poorly located. To mitigate this uncertainty with the aim of improving these hypocentral locations, we undertook the TsuJal Project, a passive seafloor seismic project conducted from April to November 2016. In addition to the Jalisco Seismic Network, 10 LCHEAPO 2000 Ocean Bottom Seismometers (OBSs) were deployed by the BO El Puma in a seafloor array from the Islas Marías Archipelago (Nayarit) to the offshore contact between the states of Colima and Michoacan. We located 445 earthquakes in four or more OBSs within the deployed array. Most of these earthquakes occurred in the contact region of the Rivera, Pacific, and Cocos plates, and a first analysis suggests the existence of three seismogenic zones (West, Center, and East) along the Rivera Transform fault that can be correlated with its morphological expression throughout the three seismogenic zones. The seismicity estimates that the Moho discontinuity is located at 10 km depth and supports earlier works regarding the West zone earthquake distribution. Subcrustal seismicity in the Central zone suggests that the Intra-Transform Spreading Basin domain is an ultra-low spreading ridge. A seismic swarm occurred during May and June 2016 between the eastern tip of the Paleo-Rivera Transform fault and the northern tip of the East Pacific Rise-Pacific Cocos Segment, illuminating some unidentified tectonic feature.

scholarly journals Tomography of crust and lithosphere in the western Indian Ocean from noise cross-correlations of land and ocean bottom seismometers

2019 ◽  
Vol 219 (2) ◽  
pp. 924-944 ◽  
Author(s):  
Sarah Hable ◽  
Karin Sigloch ◽  
Eléonore Stutzmann ◽  
Sergey Kiselev ◽  
Guilhem Barruol
Keyword(s):  
Indian Ocean ◽  
Group Velocity ◽  
Western Indian Ocean ◽  
Spreading Ridge ◽  
Ocean Bottom ◽  
Depth Range ◽  
La Réunion ◽  
Velocity Measurements ◽  
Ocean Bottom Seismometers ◽  
Cross Correlations

SUMMARY We use seismic noise cross-correlations to obtain a 3-D tomography model of SV-wave velocities beneath the western Indian Ocean, in the depth range of the oceanic crust and uppermost mantle. The study area covers 2000 × 2000 km2 between Madagascar and the three spreading ridges of the Indian Ocean, centred on the volcanic hotspot of La Réunion. We use seismograms from 38 ocean bottom seismometers (OBSs) deployed by the RHUM-RUM project and 10 island stations on La Réunion, Madagascar, Mauritius, Rodrigues, and Tromelin. Phase cross-correlations are calculated for 1119 OBS-to-OBS, land-to-OBS, and land-to-land station pairs, and a phase-weighted stacking algorithm yields robust group velocity measurements in the period range of 3–50 s. We demonstrate that OBS correlations across large interstation distances of >2000 km are of sufficiently high quality for large-scale tomography of ocean basins. Many OBSs yielded similarly good group velocity measurements as land stations. Besides Rayleigh waves, the noise correlations contain a low-velocity wave type propagating at 0.8–1.5 km s−1 over distances exceeding 1000 km, presumably Scholte waves travelling through seafloor sediments. The 100 highest-quality group velocity curves are selected for tomographic inversion at crustal and lithospheric depths. The inversion is executed jointly with a data set of longer-period, Rayleigh-wave phase and group velocity measurements from earthquakes, which had previously yielded a 3-D model of Indian Ocean lithosphere and asthenosphere. Robust resolution tests and plausible structural findings in the upper 30 km validate the use of noise-derived OBS correlations for adding crustal structure to earthquake-derived tomography of the oceanic mantle. Relative to crustal reference model CRUST1.0, our new shear-velocity model tends to enhance both slow and fast anomalies. It reveals slow anomalies at 20 km depth beneath La Réunion, Mauritius, Rodrigues Ridge, Madagascar Rise, and beneath the Central Indian spreading ridge. These structures can clearly be associated with increased crustal thickness and/or volcanic activity. Locally thickened crust beneath La Réunion and Mauritius is probably related to magmatic underplating by the hotspot. In addition, these islands are characterized by a thickened lithosphere that may reflect the depleted, dehydrated mantle regions from which the crustal melts where sourced. Our tomography model is available as electronic supplement.

scholarly journals The May 7 - 11, 2016 Earthquake Sequence at Rivera Fault Zone

2020 ◽  
Author(s):  
Francisco J Nunez-Cornu ◽  
Diego Cordoba ◽  
William L Bandy ◽  
Juan José Dañobeitia ◽  
Carlos Mortera-Gutierrez ◽  
...  
Keyword(s):  
Pressure Sensors ◽  
Velocity Model ◽  
Tectonic Stress ◽  
Seismic Network ◽  
P Wave ◽  
Earthquake Sequence ◽  
Ocean Bottom ◽  
Transform Fault ◽  
Stress Regime ◽  
Short Period

<p>The geodynamic complexity in the interaction between Rivera, Cocos and NOAM plates is mainly reflected in the high and not well located seismicity of the region. In the framework of TsuJal Project, a study of the passive seismic activity was carried out. A temporal seismic network with 25 Obsidian stations with sensor Le-3D MkIII were deploying from the northern part of Nayarit state to the south of Colima state, including the Marias Islands, in addition to the Jalisco telemetric Seismic Network, being a total of 50 seismic stations on land. Offshore, ten Ocean Bottom Seismographs type LCHEAPO 2000 with 4 channels (3 seismic short period and 1 pressure sensors) were deployed and recover by the BO El Puma from UNAM in an array from the Marias Islands to off coast of the border of Colima and Michoacan state, in the period from 19th April to 7th November 2016.</p><p>A seismic sequence started on May 7, 2016 with an earthquake Mw = 5.6 reported by CMT-Harvard, USGS and SSN at the area north of Paleo Rivera Transform fault and west of the Middle America Trench, an area with a very complex tectonics due to the interaction of Rivera, Cocos and NOAM plates.</p><p>An analysis of this earthquake sequence from May 7 to May 11 using data from OBS and adequate P-Wave velocity model for Rivera plate is presented, 87 earthquakes were located. Data from onland stations were integrated after a travel-time residual analysis.</p><p>We observed that the new location is about 50 km southwest direction, from previous one, between the Paleo Rivera Transform fault and the northern tip of the East Pacific Rise – Pacific Cocos Segment.  This area has a different tectonic stress regime.</p>

scholarly journals Microearthquake seismicity and focal mechanisms at the Rodriguez Triple Junction in the Indian Ocean using ocean bottom seismometers

2001 ◽  
Vol 106 (B12) ◽  
pp. 30689-30699 ◽  
Author(s):  
Kei Katsumata ◽  
Toshinori Sato ◽  
Junzo Kasahara ◽  
Naoshi Hirata ◽  
Ryota Hino ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Triple Junction ◽  
Focal Mechanisms ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometers ◽  
The Indian Ocean

Comparison of the S/N ratios of low-frequency hydrophones and geophones as a function of ocean depth

1981 ◽  
Vol 71 (5) ◽  
pp. 1649-1659
Author(s):  
Thomas M. Brocher ◽  
Brian T. Iwatake ◽  
Joseph F. Gettrust ◽  
George H. Sutton ◽  
L. Neil Frazer
Keyword(s):  
Nova Scotia ◽  
Continental Margin ◽  
Low Frequency ◽  
Weather Conditions ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Scotian Shelf ◽  
Ocean Bottom Seismometers ◽  
Particle Velocities ◽  
Refraction Data

abstract The pressures and particle velocities of sediment-borne signals were recorded over a 9-day period by an array of telemetered ocean-bottom seismometers positioned on the continental margin off Nova Scotia. The telemetered ocean-bottom seismometer packages, which appear to have been very well coupled to the sediments, contained three orthogonal geophones and a hydrophone. The bandwidth of all sensors was 1 to 30 Hz. Analysis of the refraction data shows that the vertical geophones have the best S/N ratio for the sediment-borne signals at all recording depths (67, 140, and 1301 m) and nearly all ranges. The S/N ratio increases with increasing sensor depth for equivalent weather conditions. Stoneley and Love waves detected on the Scotian shelf (67-m depth) are efficient modes for the propagation of noise.

scholarly journals The GITEWS ocean bottom sensor packages

2010 ◽  
Vol 10 (8) ◽  
pp. 1759-1780
Author(s):  
O. Boebel ◽  
M. Busack ◽  
E. R. Flueh ◽  
V. Gouretski ◽  
H. Rohr ◽  
...  
Keyword(s):  
Warning System ◽  
Deep Ocean ◽  
Indian Ocean Tsunami ◽  
False Alarms ◽  
Ocean Bottom ◽  
Bottom Pressure ◽  
Tsunami Early Warning ◽  
Ocean Bottom Seismometers ◽  
First Results ◽  
Sensor Package

Abstract. The German-Indonesian Tsunami Early Warning System (GITEWS) aims at reducing the risks posed by events such as the 26 December 2004 Indian Ocean tsunami. To minimize the lead time for tsunami alerts, to avoid false alarms, and to accurately predict tsunami wave heights, real-time observations of ocean bottom pressure from the deep ocean are required. As part of the GITEWS infrastructure, the parallel development of two ocean bottom sensor packages, PACT (Pressure based Acoustically Coupled Tsunameter) and OBU (Ocean Bottom Unit), was initiated. The sensor package requirements included bidirectional acoustic links between the bottom sensor packages and the hosting surface buoys, which are moored nearby. Furthermore, compatibility between these sensor systems and the overall GITEWS data-flow structure and command hierarchy was mandatory. While PACT aims at providing highly reliable, long term bottom pressure data only, OBU is based on ocean bottom seismometers to concurrently record sea-floor motion, necessitating highest data rates. This paper presents the technical design of PACT, OBU and the HydroAcoustic Modem (HAM.node) which is used by both systems, along with first results from instrument deployments off Indonesia.

Tidal Triggering of the Harmonic Noise in Ocean-Bottom Seismometers

2020 ◽  
Vol 91 (2A) ◽  
pp. 803-813 ◽  
Author(s):  
Telluri Ramakrushana Reddy ◽  
Pawan Dewangan ◽  
Lalit Arya ◽  
Pabitra Singha ◽  
Kattoju Achuta Kamesh Raju
Keyword(s):  
Spectral Analysis ◽  
Fundamental Frequency ◽  
Ocean Bottom ◽  
Automated Algorithm ◽  
Tidal Triggering ◽  
Spectral Peaks ◽  
Ocean Bottom Seismometers ◽  
Oceanic Tides ◽  
Harmonic Noise

Abstract We observed a harmonic noise (HN) in DEutscher Geräte-Pool für Amphibische Seismologie ocean-bottom seismometers (OBSs) data recorded from the Andaman–Nicobar region. The HN is characterized by sharp spectral peaks with a fundamental frequency and several overtones occurring at integer multiples of the fundamental frequency. We used an automated algorithm to quantify the occurrence of HN for the entire four-month deployment period (1 January 2014 to 30 April 2014). The algorithm detected more than 23 days of HN for some OBS stations. The spectral analysis of the hourly count of HN shows distinct lunar and solar tidal periodicities at 4.14, 6.1, 6.22, 12, and 12.4 hr as well as 13.66 days. The observed periodicities provide evidence of tidal triggering of HN. The HN is generated by the strumming of head buoys due to seafloor currents initiated by oceanic tides in the Andaman–Nicobar region.

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