Dataset Information

Mechanism of the 2015 volcanic tsunami earthquake near Torishima, Japan.

ABSTRACT: Tsunami earthquakes are a group of enigmatic earthquakes generating disproportionally large tsunamis relative to seismic magnitude. These events occur most typically near deep-sea trenches. Tsunami earthquakes occurring approximately every 10 years near Torishima on the Izu-Bonin arc are another example. Seismic and tsunami waves from the 2015 event [Mw (moment magnitude) = 5.7] were recorded by an offshore seafloor array of 10 pressure gauges, ~100 km away from the epicenter. We made an array analysis of dispersive tsunamis to locate the tsunami source within the submarine Smith Caldera. The tsunami simulation from a large caldera-floor uplift of ~1.5 m with a small peripheral depression yielded waveforms remarkably similar to the observations. The estimated central uplift, 1.5 m, is ~20 times larger than that inferred from the seismologically determined non-double-couple source. Thus, the tsunami observation is not compatible with the published seismic source model taken at face value. However, given the indeterminacy of Mzx, Mzy, and M{tensile} of a shallow moment tensor source, it may be possible to find a source mechanism with efficient tsunami but inefficient seismic radiation that can satisfactorily explain both the tsunami and seismic observations, but this question remains unresolved.

SUBMITTER: Fukao Y

PROVIDER: S-EPMC5938283 | biostudies-literature | 2018 Apr

REPOSITORIES: biostudies-literature

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Mechanism of the 2015 volcanic tsunami earthquake near Torishima, Japan.

Fukao Yoshio Y Sandanbata Osamu O Sugioka Hiroko H Ito Aki A Shiobara Hajime H Watada Shingo S Satake Kenji K

Science advances 20180404 4

Tsunami earthquakes are a group of enigmatic earthquakes generating disproportionally large tsunamis relative to seismic magnitude. These events occur most typically near deep-sea trenches. Tsunami earthquakes occurring approximately every 10 years near Torishima on the Izu-Bonin arc are another example. Seismic and tsunami waves from the 2015 event [<i>M</i><sub>w</sub> (moment magnitude) = 5.7] were recorded by an offshore seafloor array of 10 pressure gauges, ~100 km away from the epicenter. ...[more]

PMID: 29740604

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Project description:Mental health is one of the most important issues facing disaster survivors. The purpose of this study is to determine the prevalence and correlates of mental health problems in survivors of the Great East Japan Earthquake and Tsunami at 6-11 months after the disaster. The questionnaire and notification were sent to the survivors in three municipalities in the Tohoku area of the Northern part of Honshu, Japan's largest island, between September 2011 and February 2012. Questionnaires were sent to 12,772, 11,411, and 18,648 residents in the Yamada, Otsuchi, and Rikuzentakata municipalities, respectively. Residents were asked to bring the completed questionnaires to their health check-ups. A total of 11,124 or (26.0%) of them underwent health check-ups, and 10,198 were enrolled. We excluded 179 for whom a K6 score was missing and two who were both 17 years of age, which left 10,025 study participants (3,934 male and 6,091 female, mean age 61.0 years). K6 was used to measure mental health problems. The respondents were classified into moderate (5-12 of K6) and serious mental health problems (13+). A total of 42.6% of the respondents had moderate or serious mental health problems. Multivariate analysis showed that women were significantly associated with mental health problems. Other variables associated with mental health problems were: younger male, health complaints, severe economic status, relocations, and lack of a social network. An interaction effect of sex and economic status on severe mental health problems was statistically significant. Our findings suggest that mental health problems were prevalent in survivors of the Great East Japan Earthquake and Tsunami. For men and women, health complaints, severe economic status, relocations, and lack of social network may be important risk factors of poor mental health. For men, interventions focusing on economic support may be particularly useful in reducing mental health problems after the disaster.

Project description:ImportanceTrust is a core component of social cohesion, facilitating cooperation and collective action in the face of adversity and enabling survivors to remain resilient. Residential stability is an important prerequisite of developing trusting relations among community members. However, little is known about whether the movement of internally displaced persons (IDPs) after a disaster might change community relations.ObjectiveWe explored perceived changes in trust within 1 community directly impacted by the 2011 Great East Japan Earthquake and Tsunami.Design, setting, and participantsThis prospective cohort study examined survey data from 3594 residents of Iwanuma City, Japan, aged 65 years or older. Data were obtained from the Iwanuma Study-part of the Japan Gerontological Evaluation Study, a nationwide cohort study established in 2010-approximately 7 months before the disaster. All Iwanuma City residents age 65 years or older (8576 residents) were eligible to participate in 2010. The response rate was 59.0% (5058 residents). A follow-up survey was conducted in 2013, approximately 2.5 years after the disaster. Of the 4380 remaining participants who answered the baseline survey, 3594 were recontacted (follow-up rate, 82.1%). Data analysis was performed from July 1, 2019, to January 9, 2020.ExposuresThe number of temporarily relocated Iwanuma City survivors within 100 m and 250 m of a nonrelocated resident's home address.Main outcomes and measuresPerceived changes in particularized trust (ie, trusting people from the same community) and generalized trust (trusting people from other communities) measured on a 5-point Likert scale.ResultsAmong 3250 nonrelocated residents (1808 [55.6%] women; mean [SD] age, 76.5 [6.2] years) of Iwanuma City included in the analytic sample, multivariable-adjusted multinomial logistic regression analyses found that each standard deviation increase in the influx of internally displaced persons (1 SD = 11 IDPs) within 250 m of a resident's home address was associated with higher odds of a decrease in the resident's particularized and generalized trust (odds ratio, 1.17; 95% CI, 1.04-1.32).Conclusions and relevanceThe influx of IDPs in the host community appeared to be associated with an erosion of trust among locals. To avoid the erosion of social cohesion after a disaster, it may be crucial to provide opportunities for social interaction between old and new residents of communities.

Dataset Information

Mechanism of the 2015 volcanic tsunami earthquake near Torishima, Japan.

Publications

Mechanism of the 2015 volcanic tsunami earthquake near Torishima, Japan.

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