Search

The 2004 magnitude (M) 9.1 Sumatra-Andaman Islands earthquake in the Indian Ocean triggered the deadliest tsunami ever, killing more than 230,000 people. In response, the United Nations Educational, Scientific, and Cultural Organization (UNESCO) established three additional Intergovernmental Coordination Groups (ICGs) for the Tsunami and Other Coastal Hazards Early Warning System: for the Caribbean and Adjacent Regions (ICG/CARIBE-EWS), for the Indian Ocean, and for the Northeastern Atlantic, Mediterranean, and Connected Seas. Along with the ICG for the Pacific Ocean, which was established in 1965, one of the goals of the new ICGs was to improve earthquake and tsunami monitoring and early warning. This need was further demonstrated by the 2011 Great East Japan (Tōhoku-oki) earthquake and tsunami, which killed more than 20,000 people, and other destructive tsunamis that occurred in the Solomon Islands, Samoa, Tonga, Chile, Indonesia, and Peru. In response to the call to action by the UN Decade of Ocean Science for Sustainable Development (2021–2030), as well as the desired safe ocean outcome (von Hillebrandt-Andrade et al., 2021), the Intergovernmental Oceanographic Commission (IOC) of UNESCO approved the Ocean Decade Tsunami Programme in June 2021. One of its goals is to develop the capability to issue actionable alerts for tsunamis from all sources with minimum uncertainty within 10 minutes (Angove et al., 2019). While laudable, this goal presents complexities. Currently, warning depends on quick detection as well as the location and initial magnitude estimates of an earthquake that may generate a tsunami. Other factors that affect tsunamis, such as the faulting mechanism (how the faults slide past each other) and areal extent of the earthquake, currently take at least 20–30 minutes to forecast and are still subject to large uncertainties. Hence, agencies charged with tsunami early warning need to broadcast public alerts within minutes after an earthquake occurs but may struggle to meet this 10-minute goal without further technological advances, some of which are outlined in this article. To reduce loss of life through adequate tsunami warning requires global ocean-based seismic, sea level, and geodetic initiatives to detect high-impact earthquakes and tsunamis, combined with sufficient communication and education so that people know how to respond when they receive alerts and warnings. The United Nations International Strategy for Disaster Reduction defines an early warning system as “a set of capacities needed to generate and disseminate timely and meaningful warning information to enable individuals, communities, and organizations threatened by a hazard to prepare and to act appropriately and in sufficient time to reduce the possibility of harm or loss” (UNISDR, 2012). In short, a successful early warning system requires technology coupled with human factors (Kelman and Glantz, 2014). In this article, we explore case studies from Japan and Canada, where scientists are leading the way in incorporating ocean observing capabilities in their early warning systems. We also explore advancements and challenges in the Caribbean, an area with a complex tectonic environment that would benefit greatly from increased global ocean observing capabilities. We also explore physical and social science interventions necessary to reduce loss of life.

Additional file 1: Figure S1. Parameters for Chikyu on November 20, 2018. a Temporal variation of depth of the drill-bit from the sea surface. The water depth is around 2,000 m. b Temporal variation of RPM (rotation per minute). c Schematic for the geometry of two sensors, drill-bit, and the stationary zones. Figure S2. Transverse-deconvolved waveforms (TDWs) at each OBS. (a–e) Same as Figures 4b and CC in 4d, but for a OBS01, b OBS02, c OBS04, d OBS05, and e OBS06. Figure S3. Location of the center position of Chikyu and the stability of the TDWs. a Dots indicate the center position of Chikyu, which are the same as those in Fig. 2c. Red circle represents the radius of 1 m from the central location of dots. Regions are divided into eight regions; A: 1 quadrant inside 1 m, B: 2 quadrant inside 1 m, C: 3 quadrant inside 1 m, D: 4 quadrant inside 1 m, E: 1 quadrant outside 1 m, F: 2 quadrant outside 1 m, G: 3 quadrant outside 1 m, H: 4 quadrant outside 1 m. b Histogram for the Chikyu positions in the four-quadrant. The position was measured at each minute, and the number of 1-min segment during 1–57 Julian days in 2019 was counted. c (top) Waveforms at OBS03 in which the TDWs are stacked during 1–57 Julian days when the Chikyu is located in the region (black) A, (red) B, (blue) C, and (light-blue) D. (bottom) Same as the top panel, but for the region (black) E, (red) F, (blue) G, and (light-blue) H. Figure S4. Envelope functions at high and low tide. a Same as Fig. 6a, with uncertainties in pink and gray lines for the other OBSs. Arrows indicate large amplitudes at high tide at lag times between 5.5 and 7.5 s. b Same as Fig. 6b, but for OBS06.

An International Ocean Discovery Program (IODP) workshop was held at Sydney University, Australia, from 13 to 16 June 2017 and was attended by 97 scientists from 12 countries. The aim of the workshop was to investigate future drilling opportunities in the eastern Indian Ocean, southwestern Pacific Ocean, and the Indian and Pacific sectors of the Southern Ocean. The overlying regional sedimentary strata are underexplored relative to their Northern Hemisphere counterparts, and thus the role of the Southern Hemisphere in past global environmental change is poorly constrained. A total of 23 proposal ideas were discussed, with ∼ 12 of these deemed mature enough for active proposal development or awaiting scheduled site survey cruises. Of the remaining 11 proposals, key regions were identified where fundamental hypotheses are testable by drilling, but either site surveys are required or hypotheses need further development. Refinements are anticipated based upon regional IODP drilling in 2017/2018, analysis of recently collected site survey data, and the development of site survey proposals. We hope and expect that this workshop will lead to a new phase of scientific ocean drilling in the Australasian region in the early 2020s.

Figure S4. Dependence of hypocenter locations on (a) stations used, (b) use of S-wave first arrivals, and (c) strike direction of PS plate. Values in brackets represent the RMS travel time residual. Plots are along the line Aâ B shown in Fig. 2a. (PDF 82 kb)

Figure S1. Names of DONET1 stations and nodes. Gray contours represent depth distribution of the top of oceanic crust layer 2 (Citak et al. 2012). (PDF 1118Â kb)

Additional file 1. Supplementary materials of the used data for Pos wave retrieval and shear wave anisotropy measurements.

Supplementary note. (DOCX 35Â kb)

Figure S2. Comparison of hypocenter distribution with the slip deficit rate (SDR). Red circles represent hypocenters obtained in this study. SDR is after Yokota et al. (2016). (PDF 184Â kb)

2011年3月11日に，太平洋プレートと日本列島を乗せた陸側のプレートとの境界で2011年東北地方太平洋沖地震が発生した．この地震は，日本周辺では観測史上最大のマグニチュード9という巨大地震だった．本震発生後には多数の余震が発生するが，大地震発生のメカニズムを解明するためには，正確な余震分布を調べることが重要である．全国の6つの大学と海洋研究開発機構，気象庁気象研究所は，本震発生直後から共同で100台以上の海底地震計を用いて余震観測を行った．2011年6月中旬までのデータから，震源域全体で約3か月間の精度の良い震源分布が得られた．余震の震源の深さは，全体的に陸に近づくにつれて深くなっていた．震源分布からは，本震時に大きくすべったプレート境界では余震活動が低いことがわかった．上盤の陸側プレート内では余震活動が活発で，正断層型と横ずれ型が卓越していた．太平洋プレート内の余震も多くが正断層型か横ずれ型だった．このことから，日本海溝付近の太平洋プレート内の深部と上盤の陸側プレート内では，本震の発生によって応力場が圧縮場から伸張場に変化したことが示唆される．

To estimate variation of stress state and sediment consolidation in the Nankai plate subduction zone off southwest Japan, we measured the P-wave to S-wave velocity ratio (VP/VS) and S-wave splitting along the seismic line extending from the trench to the seismogenic zone. For this purpose, we used active-source seismic data recorded by multicomponent ocean bottom seismometers (OBS). Because it is difficult to identify the PS-converted reflection waveforms for each of the geological boundaries in this deep offshore region, we focused on the more easily identified PPS-refracted waveforms that register the conversion of the up-going P-waves to S-waves at the igneous crust surface. We estimated the average VP/VS ratio within the sedimentary section by using the time lag between the P-refracted waves and PPS-converted waves. This VP/VS ratio changes abruptly at the trough axis (i.e., the deformation front of the accretionary prism) arguably because of compaction associated with the accretion process. We observed relatively high VP/VS around the seismogenic megasplay fault, which may partially indicate the abnormal pore pressure and intensive fractures associated with the fault. To estimate the stress-induced fracture orientation and stress magnitude, we computed the fast S-wave polarization direction and estimated S-wave velocity anisotropy by applying the crosscorrelation method to the PPS-converted waves. To improve signal-to-noise ratio of the waveform for S-wave splitting analysis, we stacked PPS-converted waveforms on receiver gather. These anisotropic characteristics change at the seismogenic megasplay fault: the fast polarization direction is nearly parallel to the subduction direction seaward of the megasplay fault and is perpendicular to the subduction direction landward of the megasplay fault. This velocity anisotropy is especially strong around the megasplay fault. These results imply that the preferred fracture orientation, as well as the principal stress orientation, is oblique to the direction of plate subduction near the megasplay fault.

[CRUISE REPORT] This document is a preliminary report of KR16-05 Leg1 on R/V KAIREI from 2016-03-23 to 2016-03-30, KR16-05 Leg2 on R/V KAIREI from 2016-04-02 to 2016-04-20 and KR16-05 Leg3 on R/V KAIREI from 2016-04-21 to 2016-05-26.

application/pdf

[CRUISE REPORT] This document is a preliminary report of KR13-01 on R/V KAIREI from 2013-01-09 to 2013-01-18.

[CRUISE REPORT] This document is a preliminary report of KY08-E03 on R/V KAIYO from 2008-11-06 to 2008-11-21.

[CRUISE REPORT] This document is a preliminary report of KR08-09 on R/V KAIREI from 2008-07-27 to 2008-08-11.