The 2011 Mw 9.0 Tohoku‐oki earthquake is one of the world's best‐recorded ruptures. In the aftermath of this devastating event, it is important to learn from the complete record. We describe the ...state of knowledge of the megathrust earthquake generation process before the earthquake, and what has been learned in the decade since the historic event. Prior to 2011, there were a number of studies suggesting the potential of a great megathrust earthquake in NE Japan from geodesy, geology, seismology, geomorphology, and paleoseismology, but results from each field were not enough to enable a consensus assessment of the hazard. A transient unfastening of interplate coupling and increased seismicity were recognized before the earthquake, but did not lead to alerts. Since the mainshock, follow‐up studies have (1) documented that the rupture occurred in an area with a large interplate slip deficit, (2) established large near‐trench coseismic slip, (3) examined structural anomalies and fault‐zone materials correlated with the coseismic slip, (4) clarified the historical and paleoseismic recurrence of M∼9 earthquakes, and (5) identified various kinds of possible precursors. The studies have also illuminated the heterogeneous distribution of coseismic rupture, aftershocks, slow earthquakes and aseismic afterslip, and the enduring viscoelastic response, which together make up the complex megathrust earthquake cycle. Given these scientific advances, the enhanced seismic hazard of an impending great earthquake can now be more accurately established, although we do not believe such an event could be predicted with confidence.
Plain Language Summary
The Mw 9 Tohoku‐oki earthquake was one of the most disastrous earthquakes in recent history. In this review, we first clarify the knowledge of the earthquake and tsunami potential before the earthquake. Pre‐Tohoku‐oki studies partly recognized the potential of Mw 8 or larger earthquakes. However, the knowledge based on different types of observations was incomplete and the occurrence of such a great event was not considered in the official earthquake probabilities. The improved understanding of earthquake‐cycle and rupture processes since the Tohoku‐oki earthquake advanced the leading edge of efforts to characterize megathrust earthquake hazards. We can summarize the lessons as follows. (1) The incorporation of interdisciplinary research is essential to advance our understanding of the processes underlying the occurrence of earthquakes. (2) The recognition of earthquake potential informed by geologic evidence extending beyond available instrumental records is essential for assessing the largest possible earthquake in a subduction zone. (3) The development of advanced scientific infrastructure, especially ocean‐bottom observations is necessary to evaluate earthquake potential and monitor dynamic megathrust fault‐zone processes. (4) Although post‐Tohoku‐oki studies have better characterized the hazard and a number of possible precursors have been identified, the confident prediction of such events appears impossible in the near future.
Key Points
The lessons learned in the last decade highlight more realistic estimation of seismic hazard and importance of interdisciplinary study
Pre‐2011 studies based on a variety of evidence did not result in a consensus assessment of the great‐earthquake hazard
Despite the precursory foreshocks and slow slip and improved monitoring capabilities, prediction of such events still appears impossible
Investigating slow earthquake activity in subduction zones provides insight into the slip behavior of megathrusts, which can provide important clues about the rupture extent of future great ...earthquakes. Using the S-net ocean-bottom seismograph network along the Japan Trench, we mapped a detailed distribution of tectonic tremors, which coincided with very-low-frequency earthquakes and a slow slip event. Compiling these and other related observations, including repeating earthquakes and earthquake swarms, we found that the slow earthquake distribution is complementary to the Tohoku-Oki earthquake rupture. We used our observations to divide the megathrust in the Japan Trench into three along-strike segments characterized by different slip behaviors. We found that the rupture of the Tohoku-Oki earthquake, which nucleated in the central segment, was terminated by the two adjacent segments.
The Sea of Marmara accommodates segments of the North Anatolian Fault (NAF) in Turkey and remains the only part of the western NAF that has not ruptured during the last century. At its nearest, the ...segment is ~20 km from Istanbul, the largest city in Turkey. Thus, it is important to understand the locking state of the fault, since it illuminates the strain accumulation rate along the fault segments, which in turn is an important input parameter in seismic hazard studies. To infer the interplate locking state, we used repeating earthquakes that indicate fault creep in the surrounding area using long-term (April 2005 to May 2013) seismic observations at 12 broadband seismic stations operated by Bogazici University Kandilli Observatory and Earthquake Research Institute. We defined repeating earthquakes from waveform coherences that were >0.95 for 40-second-long waveforms of the vertical component. Using the selection procedure, we found 21 repeating earthquakes with magnitude 2.3 to 3.2 that are grouped into 9 sequences. They are distributed along the main NAF, comprising three groups of activity, one group in the Sea of Marmara and a group either side to the east and west. The three groups are located near the boundary of previous large earthquake ruptures, suggesting relatively weak coupling there. We also estimated the fault creep rate from the cumulative slip of the repeating earthquakes using a scaling relationship between repeating earthquakes' moment and slip. The slip rate for these three groups are similar (3–4 cm/yr) and comparable to, albeit slightly higher than, those expected from global plate models (~2.4 cm/yr). This suggests relatively weak locking around the groups. The relocation results of the repeating earthquake hypocenters in the Sea of Marmara suggest the creep is occurring at 10 to 20 km depth. These results suggest heterogeneous coupling in the segment.
•Repeating earthquakes along the North Anatolian Fault were identified.•The repeaters are located near the rupture boundaries of past earthquakes.•The creep rates from the repeater data are similar to that of relative plate motion.•The repeaters in the Sea of Marmara suggest creeping at 10 to 20 km depth.
The effect of graft-versus-host disease (GVHD) on transplant outcomes after unrelated cord blood transplantation (UCBT) has not been fully elucidated. We analyzed the impact of acute and chronic GVHD ...on outcomes in adult patients with acute leukemia or myelodysplastic syndrome who underwent their first UCBT (n=2558). The effect of GVHD on outcomes was analyzed after adjusting for other significant variables. The occurrence of GVHD was treated as a time-dependent covariate. The occurrence of grade 1-2 or 3-4 acute GVHD was significantly associated with a lower relapse rate. Grade 3-4 acute GVHD was associated with a higher risk of non-relapse and overall mortality than no acute GVHD, whereas grade 1-2 acute GVHD was associated with a lower risk of non-relapse and overall mortality than no acute GVHD. Limited or extensive chronic GVHD was significantly associated with a lower relapse rate. Limited chronic GVHD was associated with a lower overall and non-relapse mortality than no chronic GVHD. In conclusion, mild acute or chronic GVHD was associated not only with a low risk of relapse but also with a low risk of non-relapse mortality, and provides a survival benefit in UCBT.
This paper presents a quick and accurate power control method for a zone-control induction heating (ZCIH) system consisting of multiple working coils connected to multiple H-bridge inverters. A ...uniform temperature profile can be achieved by adjusting the current in each working coil. This paper proposes a new current control method based on a circuit model using real and imaginary (Re-Im) current/voltage components. The method detects and controls the Re-Im components of the coil current instead of the current amplitude and phase angle. As a result, the proposed method enables the inverters to control the coil current independently from the others. Experiments using a six-coil ZCIH system are conducted to verify the validity of the proposed method. The experimental results confirmed that the proposed method makes it possible to improve the stability of the current feedback control, not only in steady states but also in transient states.
One of the important issues on the GPS‐acoustic (GPS‐A) observation for sea bottom positioning is how to address the horizontal heterogeneity of the sound speed in oceans. This study presents an ...analysis method of GPS‐A data in the presence of a sloping sound speed structure. By applying this method and revising the analysis scheme to make full use of existing data, we reevaluated the horizontal postseismic deformations occurring ~1.5–5 years after the 2011 Tohoku earthquake. The revised horizontal movements have more uniform directions and rates between neighboring sites, suggesting enhancement of the array positioning accuracy. The revised displacement rate of the site on the incoming Pacific plate, located ~100 km northeast of the main rupture zone, was decreased significantly; it was only slightly, by 1.4 cm/year larger than the global motion of the Pacific plate, suggesting a relatively small effect of viscoelastic relaxation. The horizontal movements of the near‐trench sites above the main rupture zone were generally landward and were significantly faster than the Pacific plate motion, indicating a viscoelastic relaxation of 5–10 cm/year. The distribution of the fast landward movements peaked near 38°N at an updip of the mainshock hypocenter and extended significantly farther to the north than to the south. This implies the existence of a secondary coseismic slip patch in the northern area in addition to a primary slip patch at ~38°N. The occurrence of episodic slow slip in early 2015 to the north of the main rupture zone was also verified from the GPS‐A analyses.
Key Points
We present a new analysis method of GPS‐acoustic observation data for seafloor positioning in the presence of sloping sound speed structure
The application to the 2011 Tohoku earthquake demonstrate enhanced position accuracy by the spatially coherent postseismic movements
The occurrence of episodic slow slip in 2015, which has been inferred from repeating earthquakes, was also verified from our observations
Strong magnetic fields, synchrotron emission, and Compton scattering are omnipresent in compact celestial X-ray sources. Emissions in the X-ray energy band are consequently expected to be linearly ...polarized. X-ray polarimetry provides a unique diagnostic to study the location and fundamental mechanisms behind emission processes. The polarization of emissions from a bright celestial X-ray source, the Crab, is reported here for the first time in the hard X-ray band (~20-160 keV). The Crab is a complex system consisting of a central pulsar, a diffuse pulsar wind nebula, as well as structures in the inner nebula including a jet and torus. Measurements are made by a purpose-built and calibrated polarimeter, PoGO+. The polarization vector is found to be aligned with the spin axis of the pulsar for a polarization fraction, PF = (20.9 ± 5.0)%. This is higher than that of the optical diffuse nebula, implying a more compact emission site, though not as compact as, e.g., the synchrotron knot. Contrary to measurements at higher energies, no significant temporal evolution of phase-integrated polarisation parameters is observed. The polarization parameters for the pulsar itself are measured for the first time in the X-ray energy band and are consistent with observations at optical wavelengths.
The most frequently used method to identify mutations induced by a commonly used mutagen, EMS (ethyl methane sulfonate), in Arabidopsis thaliana has been map-based cloning. The first step of this ...method is crossing a mutant with a plant of another accession as it requires polymorphisms between accessions for linkage analysis. Therefore, to perform the method routinely, it is greatly preferred to use accession combinations between which enough polymorphisms are already known. Further, it requires laborious examination of a large number of F₂ recombinants using many markers to detect each polymorphism. After linkage analysis narrows down the chromosomal region containing the causal mutation, sequencing candidate genes one by one within the region is necessary until the mutation is finally identified. Overall, this method is generally time-consuming and labor intensive, and it becomes harder when multiple loci are involved in phenotypes. A few recent reports showed that causal mutations induced by EMS could be identified by deep-sequencing technologies with less labor compared with the conventional method when mutants were generated in the Arabidopsis reference Columbia background whose genome organization is well known. Here we report that we succeeded in rapid identification of EMS-induced causal mutations in a non-reference accession background, whose whole genome sequence is not publicly available, using one round of whole genome sequencing. Moreover, in our case, we could monitor the causal locus and the transgenic reporter locus simultaneously, implying that this methodology could theoretically be applicable to analyzing even complex traits. We describe the pipeline of this methodology and discuss its characteristics.
This paper presents a phase angle control method of high-frequency resonant currents in a zone-control induction heating (ZCIH) system, which consists of split working coils and multiple inverters. ...The ZCIH system controls the amplitude of each coil current to make the temperature distribution on the workpiece uniform. The amplitude of the coil current can be controlled in a wide range when its phase angle is adjusted to be the same with other coil currents. This paper theoretically derives the phase-angle change of the coil current in transient states, and reveals that the phase-angle change can be considered as a first-order response. A phase-angle controller was designed and examined in experiments using a two-zone ZCIH system. It is clarified that the phase angle control makes it possible to adjust the current phase angle not only in steady states but also in transient states.
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