Comparison of mid‐oceanic earthquake epicentral differences of travel time, centroid locations, and those determined by autonomous underwater hydrophone arrays

Pan, Jianfeng

doi:10.1029/2003jb002785

Cited by 22 publications

(24 citation statements)

References 43 publications

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“…This mechanism is similar to that proposed by Johnson et al for the generation of abyssal T phases, 12 and T phases of this type have most recently been observed by Slack et al 19 and Pan and Dziewonski. 20 However, in our case the signal enters the water column near the receiver; a simple calculation of the travel time indicates that this component does not propagate primarily as water borne energy that was scattered into the sound channel near the earthquake source.…”

Section: T-phase Propagation Modelmentioning

confidence: 98%

The directionality of acoustic T-phase signals from small magnitude submarine earthquakes

Chapman

Marrett

2006

The Journal of the Acoustical Society of America

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Acoustic transients radiated from small magnitude undersea earthquakes were studied in an experiment carried out using a towed horizontal line array operating in the South Fiji Basin. The transient signals consisted of P, S, and T phases, with the T-phase signal from each earthquake lasting up to 7 min. The directionality of the T-phase signal was determined by processing the array hydrophone data with a conventional beamformer. The weakest part of the signal arrived first on a direct bearing between the earthquake source and the array. However, subsequent stronger components arrived from different directions farther south of the source, in a region where a number of seamounts and ridges rose within the sound channel. A simple model based on ray path travel times for elastic wave travel in the earth and acoustic wave propagation in the water suggests that the later components of the T-phase signal were radiated into the water by downslope propagation from the seamounts and ridges. The initial weaker components may be scattered into the sound channel by leakage from the P and S phases relatively close to the array.

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Section: T-phase Propagation Modelmentioning

confidence: 98%

The directionality of acoustic T-phase signals from small magnitude submarine earthquakes

Chapman

Marrett

2006

The Journal of the Acoustical Society of America

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“…concluded that the hydroacoustic data improve the completeness level of the earthquake catalog for the MAR by about 1.5–2.0 orders of magnitude, yielding a magnitude of completeness of about M = 2.5. With the improved detection and the improved location accuracy provided by hydroacoustic techniques (errors of a few kilometers [ Dziak et al , 2004; Pan and Dziewonski , 2005]), it has been possible to address a number of diverse geologic problems [e.g., Bohnenstiehl et al , 2002; Dziak et al , 2004; Escartín et al , 2008; Simão et al , 2010; Smith et al , 2003; Williams et al , 2006] including the seismic characteristics of inside corner highs and core complexes such as the Atlantic Massif [ Escartín et al , 2008; Williams et al , 2006].…”

Section: Seismic Experiments and Data Analysismentioning

confidence: 99%

Seismicity of the Atlantis Massif detachment fault, 30°N at the Mid‐Atlantic Ridge

Collins

Smith

McGuire

2012

Geochem Geophys Geosyst

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[1] At the oceanic core complex that forms the Atlantis Massif at 30 N on the Mid-Atlantic Ridge, slip along the detachment fault for the last 1.5-2 Ma has brought lower crust and mantle rocks to the seafloor. Hydroacoustic data collected between 1999 and 2003 suggest that seismicity occurred near the top of the Massif, mostly on the southeastern section, while detected seismicity along the adjacent ridge axis was sparse. In 2005, five short-period ocean bottom seismographs (OBS) were deployed on and around the Massif as a pilot experiment to help constrain the distribution of seismicity in this region. Analysis of six months of OBS data indicates that, in contrast to the results of the earlier hydroacoustic study, the vast majority of the seismicity is located within the axial valley. During the OBS deployment, and within the array, seismicity was primarily composed of a relatively constant background rate and two large aftershock sequences that included 5 teleseismic events with magnitudes between 4.0 and 4.5. The aftershock sequences were located on the western side of the axial valley adjacent to the Atlantis Massif and close to the ridge-transform intersection. They follow Omori's law, and constitute more than half of the detected earthquakes. The OBS data also indicate a low but persistent level of seismicity associated with active faulting within the Atlantis Massif in the same region as the hydroacoustically detected seismicity. Within the Massif, the data indicate a north-south striking normal fault, and a left-lateral, strike-slip fault near a prominent, transform-parallel, north-facing scarp. Both features could be explained by changes in the stress field at the inside corner associated with weak coupling on the Atlantis transform. Alternatively, the normal faulting within the Massif might indicate deformation of the detachment surface as it rolls over to near horizontal from an initial dip of about 60 beneath the axis, and the strike-slip events may indicate transform-parallel movement on adjacent detachment surfaces.

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“…Moreover, because our hydroacoustic location technique utilizes oceanographic sound velocity models, which are well known and adjusted for seasonal variations, and our array geometry provides good azimuthal coverage of the MAR, the magnitude of completeness for hydroacoustic arrays is expected to be an order of magnitude lower than what can be achieved using regional or teleseismic earthquake monitoring. In remote areas from land‐based network, the locations of earthquakes recorded by four or more hydrophones are generally more accurate than land‐based derived locations [ Bohnenstiehl and Tolstoy , 2003; Pan and Dziewonski , 2005]; added to a lower detection threshold, hydrophone arrays are thus fully suitable for detailed studies of the low‐level seismicity.…”

Section: The Sirena Experimentsmentioning

confidence: 99%

Spatiotemporal distribution of the seismicity along the Mid‐Atlantic Ridge north of the Azores from hydroacoustic data: Insights into seismogenic processes in a ridge–hot spot context

Goslin¹,

Perrot²,

Royer³

et al. 2012

Geochem Geophys Geosyst

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[1] The seismicity of the North Atlantic was monitored from May 2002 to September 2003 by the 'SIRENA array' of autonomous hydrophones. The hydroacoustic signals provide a unique data set documenting numerous low-magnitude earthquakes along the section of the Mid-Atlantic Ridge (MAR) located in a ridge-hot spot interaction context. During the experiment, 1696 events were detected along the MAR axis between 40°N and 51°N, with a magnitude of completeness level of m b ≈ 2.4. Inside the array, location errors are in the order of 2 km, and errors in the origin time are less than 1 s. From this catalog, 15 clusters were detected. The distribution of source level (SL) versus time within each cluster is used to discriminate clusters occurring in a tectonic context from those attributed to non-tectonic (i.e. volcanic or hydrothermal) processes. The location of tectonic and non-tectonic sequences correlates well with regions with positive and negative Mantle Bouguer Anomalies (MBAs), indicating the presence of thinner/colder and thicker/ warmer crust respectively. At the scale of the entire array, both the complete and declustered catalogs derived from the hydroacoustic signals show an increase of the seismicity rate from the Azores up to Copyright 2012 by the American Geophysical Union 1 of 15 43°30′N suggesting a diminishing influence of the Azores hot spot on the ridge-axis temperature, and well correlated with a similar increase in the along-axis MBAs. The comparison of the MAR seismicity with the Residual MBA (RMBA) at different scales leads us to think that the low-magnitude seismicity rates are directly related to along-axis variations in lithosphere rheology and temperatures.

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Comparison of mid‐oceanic earthquake epicentral differences of travel time, centroid locations, and those determined by autonomous underwater hydrophone arrays

Cited by 22 publications

References 43 publications

The directionality of acoustic T-phase signals from small magnitude submarine earthquakes

The directionality of acoustic T-phase signals from small magnitude submarine earthquakes

Seismicity of the Atlantis Massif detachment fault, 30°N at the Mid‐Atlantic Ridge

Spatiotemporal distribution of the seismicity along the Mid‐Atlantic Ridge north of the Azores from hydroacoustic data: Insights into seismogenic processes in a ridge–hot spot context

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