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Kazushige Obara - One of the best experts on this subject based on the ideXlab platform.
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characteristics of short term slow slip events estimated from deep low frequency tremors in shikoku japan
Journal of Geophysical Research, 2010Co-Authors: Tetsuya Hirose, Yoshihiro Hiramatsu, Kazushige ObaraAbstract:[1] We have investigated the characteristics of short-term slow slip events (SSEs), Recurrence Interval and size distribution, and the slip rate at the transition zone on the plate interface beneath the Shikoku region, Japan, using nonvolcanic deep low frequency (DLF) tremors. On the basis of a proportional relationship between the seismic moment of SSE observed geodetically and the total size of DLF tremors of the corresponding episode, we estimated the seismic moment due to the slip on the plate interface from the DLF tremors and a temporal variation in the cumulative seismic moment. The Recurrence Interval of major short-term SSEs is ∼6 months in the western area and 3 months in the central and the eastern areas. The size distribution of short-term SSEs as well as DLF tremors is approximated by an exponential law rather than by a power law, showing a different scaling for regular earthquakes. The average slip rate at the transition zone estimated from the cumulative seismic moment with time of SSEs is 4.2 cm/yr, 3.3 cm/yr, and 4.9 cm/yr in the western, central, and eastern areas, respectively. These values compensate for the difference between the convergence rate at the trench and the slip deficit rate at the transition zone of the subducting Philippine Sea plate. In other words, the slip rate estimated from the DLF tremors provides a constraint of the slip deficit rate at the transition zone on the plate interface.
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non volcanic deep low frequency tremors accompanying slow slips in the southwest japan subduction zone
Tectonophysics, 2006Co-Authors: Kazushige Obara, Hitoshi HiroseAbstract:Non-volcanic deep low-frequency tremors in southwest Japan exhibit a strong temporal and spatial correlation with slow slip detected by the dense seismic network. The tremor signal is characterized by a low-frequency vibration with a predominant frequency of 0.5–5 Hz without distinct P- or S-wave onset. The tremors are located using the coherent pattern of envelopes over many stations, and are estimated to occur near the transition zone on the plate boundary on the forearc side along the strike of the descending Philippine Sea plate. The belt-like distribution of tremors consists of many clusters. In western Shikoku, the major tremor activity has a Recurrence Interval of approximately six months, with each episode lasting over a week. The tremor source area migrates during each episode along the strike of the subducting plate with a migration velocity of about 10 km/day. Slow slip events occur contemporaneously with this tremor activity, with a coincident estimated source area that also migrates during each episode. The coupling of tremor and slow slip in western Shikoku is very similar to the episodic tremor and slip phenomenon reported for the Cascadia margin in northwest North America. The duration and Recurrence Interval of these episodes varies between tremor clusters even on the same subduction zone, attributable to regional difference in the frictional properties of the plate interface.
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episodic slow slip events accompanied by non volcanic tremors in southwest japan subduction zone
Geophysical Research Letters, 2004Co-Authors: Kazushige Obara, Hitoshi Hirose, Fumio Yamamizu, Keiji KasaharaAbstract:[1] Episodic slow slip events have been recognized by means of tilt changes in the western Shikoku area, southwest Japan. The crustal tilt deformation was observed repeatedly with a Recurrence Interval of approximately six months coincident with the occurrences of major non-volcanic deep tremor activities in this area. Observed tilt changes can be explained by slow slip events occurring around the source area of tremors. In each episode, the source of the slow slip event and tremor migrate simultaneously. The spatial and temporal coincidence of tremors and slow slip events indicates that they both may be coupling phenomena reflecting the stress accumulation process at the subducting plate.
Hitoshi Hirose - One of the best experts on this subject based on the ideXlab platform.
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non volcanic deep low frequency tremors accompanying slow slips in the southwest japan subduction zone
Tectonophysics, 2006Co-Authors: Kazushige Obara, Hitoshi HiroseAbstract:Non-volcanic deep low-frequency tremors in southwest Japan exhibit a strong temporal and spatial correlation with slow slip detected by the dense seismic network. The tremor signal is characterized by a low-frequency vibration with a predominant frequency of 0.5–5 Hz without distinct P- or S-wave onset. The tremors are located using the coherent pattern of envelopes over many stations, and are estimated to occur near the transition zone on the plate boundary on the forearc side along the strike of the descending Philippine Sea plate. The belt-like distribution of tremors consists of many clusters. In western Shikoku, the major tremor activity has a Recurrence Interval of approximately six months, with each episode lasting over a week. The tremor source area migrates during each episode along the strike of the subducting plate with a migration velocity of about 10 km/day. Slow slip events occur contemporaneously with this tremor activity, with a coincident estimated source area that also migrates during each episode. The coupling of tremor and slow slip in western Shikoku is very similar to the episodic tremor and slip phenomenon reported for the Cascadia margin in northwest North America. The duration and Recurrence Interval of these episodes varies between tremor clusters even on the same subduction zone, attributable to regional difference in the frictional properties of the plate interface.
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episodic slow slip events accompanied by non volcanic tremors in southwest japan subduction zone
Geophysical Research Letters, 2004Co-Authors: Kazushige Obara, Hitoshi Hirose, Fumio Yamamizu, Keiji KasaharaAbstract:[1] Episodic slow slip events have been recognized by means of tilt changes in the western Shikoku area, southwest Japan. The crustal tilt deformation was observed repeatedly with a Recurrence Interval of approximately six months coincident with the occurrences of major non-volcanic deep tremor activities in this area. Observed tilt changes can be explained by slow slip events occurring around the source area of tremors. In each episode, the source of the slow slip event and tremor migrate simultaneously. The spatial and temporal coincidence of tremors and slow slip events indicates that they both may be coupling phenomena reflecting the stress accumulation process at the subducting plate.
Thomas K Rockwell - One of the best experts on this subject based on the ideXlab platform.
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refining seismic parameters in low seismicity areas by 3d trenching the alhama de murcia fault se iberia
Tectonophysics, 2016Co-Authors: Marta Ferrater, Maria Ortuno, E Masana, Raimon Pallas, Hector Perea, Stephane Baize, Eduardo Garciamelendez, J J Martinezdiaz, Anna Echeverria, Thomas K RockwellAbstract:Three-dimensional paleoseismology in strike-slip faults with slip rates less than 1 mm per year involves a great methodological challenge. We adapted 3D trenching to track buried channels offset by the Alhama de Murcia seismogenic left-lateral strike-slip fault (SE Iberia). A fault net slip of 0.9 ± 0.1 mm/yr was determined using statistical analysis of piercing lines for one buried channel, whose age is constrained between 15.2 ± 1.1 ka and 21.9–22.3 cal BP. This value is larger and more accurate than the previously published slip rates for this fault. The minimum number of five paleo-earthquakes identified since the deposition of dated layers suggests a maximum average Recurrence Interval of approximately 5 ka. The combination of both seismic parameters yields a maximum slip per event between 5.3 and 6.3 m. We show that accurately planned trenching strategies and data processing may be key to obtaining robust paleoseismic parameters in low seismicity areas.
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a 21 event 4 000 year history of surface ruptures in the anza seismic gap san jacinto fault and implications for long term earthquake production on a major plate boundary fault
Pure and Applied Geophysics, 2015Co-Authors: Thomas K Rockwell, Timothy E Dawson, Jeri Young Benhorin, Gordon G SeitzAbstract:Paleoseismic work completed at Hog Lake on the San Jacinto Fault (SJF) near Anza, California, indicates that at least 21 surface ruptures have occurred in the Anza Seismic gap over the past 4,000 years. The ages of the ruptures are constrained by 111 radiocarbon dates, 97 of which fall in stratigraphic order. The average Recurrence Interval for all ruptures for this period is about 185 ± 105 years, although some ruptures, such as occurred in the April 1918 earthquake, caused only minor displacement. We rate the expression of each interpreted event in each of the twelve developed field exposures presented in this work by assigning numeric values for the presence of different criteria that indicate rupture to a paleo-ground surface. Weakly expressed ruptures, for example the deformation we interpret to be the result of the historical 1918 earthquake, received low scores and are interpreted as smaller earthquakes. From this analysis, we infer that at least fifteen of the identified ruptures are indicative of large earthquakes similar to the penultimate earthquake, inferred to be the M w 7.3 22 November 1800 earthquake. The adjusted Recurrence Interval for large earthquakes lengthens to approximately 254 years. Comparison with the rupture history at the Mystic Lake paleoseismic site on the Claremont strand indicates that it is plausible that several of the large ruptures identified at Hog Lake could have jumped the Hemet step-over at Mystic Lake and continued on the Claremont strand (or vice versa), but most of the event ages do not match between the two sites, indicating that most ruptures do not jump the step. Finally, comparison with San Andreas Fault ruptures both to the north and south of its juncture with the SJF suggest that some northern SJF ruptures identified at Mystic Lake may correlate with events identified at Wrightwood, but that these northern ruptures have no match at Hog Lake and can not indicate rupture of the entire SJF onto the SAF.
Robert E Bristow - One of the best experts on this subject based on the ideXlab platform.
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secondary cytoreductive surgery for localized recurrent epithelial ovarian cancer analysis of prognostic factors and survival outcome
Cancer, 2007Co-Authors: Ritu Salani, Antonio Santillan, Mariana L Zahurak, Robert L Giuntoli, Ginger J Gardner, Deborah K Armstrong, Robert E BristowAbstract:BACKGROUND. The objective of this study was to evaluate the role of secondary cytoreductive surgery in the outcome of patients who had recurrent epithelial ovarian carcinoma that was limited to ≤5 Recurrence sites within the abdomen or pelvis on preoperative imaging studies and attempt to define selection criteria associated with improved survival, with specific attention to the number of lesions suspicious for recurrent disease. METHODS. Patients who underwent secondary surgical cytoreduction for recurrent epithelial ovarian cancer between September 1997 and March 2005 were identified retrospectively from tumor registry databases. Study inclusion criteria required a complete clinical response to primary therapy, ≥12 months between initial diagnosis and Recurrence, and ≤5 Recurrence sites on preoperative imaging studies. Univariate and multivariate logistic regression analyses were used to evaluate the effect of clinicopathologic variables on overall postRecurrence survival. RESULTS. Fifty-five patients met the study inclusion criteria. The median patient age at Recurrence was 57.7 years, and the median diagnosis-to-Recurrence Interval was 32 months (range, 12–164 months). Complete cytoreduction was achieved in 41 patients (74.5%). On multivariate analysis, the statistically significant and independent predictors of overall survival were a diagnosis-to-Recurrence Interval ≥18 months (median survival, 49 months vs 3 months; P < .01), the number of radiographic Recurrence sites (median survival, 50 months for patients with 1 or 2 sites vs 12 months for patients with 3 to 5 sites; P < .03), and residual disease (median survival, 50 months for patients with no macroscopic residual disease vs 7.2 months for patients with macroscopic residual disease; P < .01). Age, tumor grade, histology, CA-125 level, ascites, and tumor size were not associated significantly with survival. CONCLUSIONS. The current data supported the definition of localized recurrent ovarian cancer as patients with 1 or 2 radiographic Recurrence sites. In this select population, a diagnosis-to-Recurrence Interval ≥18 months and complete secondary surgical cytoreduction, which was achievable in the majority of patients, were associated with a median postRecurrence survival of approximately 50 months. Cancer 2007. © 2007 American Cancer Society.
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secondary cytoreductive surgery for localized recurrent epithelial ovarian cancer analysis of prognostic factors and survival outcome
Journal of Clinical Oncology, 2006Co-Authors: Ritu Salani, Antonio Santillan, Mariana L Zahurak, Robert L Giuntoli, Ginger J Gardner, Deborah K Armstrong, Robert E BristowAbstract:5029 Background: To evaluate prognostic factors and survival outcome of patients undergoing secondary cytoreductive surgery for recurrent epithelial ovarian cancer with ≤ 5 sites of Recurrence on pre-operative imaging studies. Methods: Patients undergoing secondary cytoreduction for recurrent epithelial ovarian carcinoma between 9/1997–3/2005 were retrospectively identified from tumor registry databases. Inclusion required: complete clinical response to primary therapy, ≥12 months between initial diagnosis and Recurrence, and ≤5 Recurrence sites on pre-operative imaging studies. Univariate and multivariate logistic regression analyses were used to evaluate the effect of clinico-pathologic variables on overall post-Recurrence survival. Results: Fifty-five patients met study inclusion criteria. The median age at Recurrence was 57.7 years and the median diagnosis-to-Recurrence Interval was 32 months (range 12 to 164 months). Complete cytoreduction was achieved in 41 patients (74.5%). On multivariate analysis...
John Beavan - One of the best experts on this subject based on the ideXlab platform.
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a large slow slip event on the central hikurangi subduction interface beneath the manawatu region north island new zealand
Geophysical Research Letters, 2006Co-Authors: L M Wallace, John BeavanAbstract:[1] We present continuous GPS observations of a surface deformation episode in the Manawatu region of the North Island, New Zealand, lasting 18 months from January 2004 to June 2005. We invert vertical and horizontal displacements of GPS sites during the event for slow slip on the Hikurangi subduction thrust. We find that up to 350 mm of slip occurred on the thrust in the transition zone between strong interseismic coupling and aseismic creep. If the entire slip in the Manawatu slow slip event had occurred instantaneously, it would have resulted in an Mw 7.0 earthquake. Given the large amount of slip, we expect that the Recurrence Interval for similar slow slip events may be ten years or more.
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slow slip on the northern hikurangi subduction interface new zealand
Geophysical Research Letters, 2005Co-Authors: Annie Douglas, John Beavan, L M Wallace, J TownendAbstract:[1] In October 2002, a surface displacement episode of 20–30 mm magnitude was observed over a ∼10 day period on two continuous Global Positioning System (GPS) instruments near Gisborne, North Island, New Zealand. We interpret this to result from slow slip on the northern Hikurangi subduction interface. Using ten years of regional campaign GPS (1995–2004) and recent continuous GPS data, we estimate the Recurrence Interval for similar events to be 2–3 yrs. In November 2004, a similar slow slip event occurred within this Recurrence period. The 2002 event can be modeled by ∼18 cm of slow slip near the down-dip end of the seismogenic zone on the subduction interface offshore of Gisborne. The campaign GPS data show that the 2002 slow slip event had little effect on regional strain patterns.
