Hiroshi Tsuruoka

Propagation of slow slip leading up to the 2011 mw 9.0 tohoku-oki earthquake

Before Tohoku-Oki Recordings by Japans dense seismic network in the days and weeks before the 2011 Mw 9.0 Tohoku-Oki earthquake provide an opportunity to interrogate what caused the dynamic rupture of one of the largest earthquakes on record. Using a method to extract small earthquakes that are often obscured by overlapping seismic waves, Kato et al. (p. 705, published online 19 January) identified over a thousand small repeating earthquakes that migrated slowly toward the hypocenter of the main rupture. Based on the properties of these foreshocks, the plate interface experienced two sequences of slow slip, the second of which probably contributed a substantial amount of stress and may have initiated the nucleation of the main shock. Two sequences of slow slip preceded and migrated toward the main rupture. Many large earthquakes are preceded by one or more foreshocks, but it is unclear how these foreshocks relate to the nucleation process of the mainshock. On the basis of an earthquake catalog created using a waveform correlation technique, we identified two distinct sequences of foreshocks migrating at rates of 2 to 10 kilometers per day along the trench axis toward the epicenter of the 2011 moment magnitude (Mw) 9.0 Tohoku-Oki earthquake in Japan. The time history of quasi-static slip along the plate interface, based on small repeating earthquakes that were part of the migrating seismicity, suggests that two sequences involved slow-slip transients propagating toward the initial rupture point. The second sequence, which involved large slip rates, may have caused substantial stress loading, prompting the unstable dynamic rupture of the mainshock.

Analysis of the Completeness Magnitude and Seismic Network Coverage of Japan

Abstract A reliable estimate of completeness magnitude, M c , above which all earthquakes are considered to be detected by a seismic network, is vital for seismicity-related studies. We show a comprehensive analysis of M c in Japan. We use the catalog maintained by the Japan Meteorological Agency (JMA) and also available information on seismic stations that report to JMA. For computing M c , we adopt a commonly used method based on the Gutenberg–Richter frequency-magnitude law. Presently, M c =1.0 might be typical in the mainland, but to have a complete catalog, one needs to use earthquakes with magnitudes of 1.9 or larger. Comparison with the Southern California Seismic Network (SCSN) suggests that the recent event detectability in the mainland generally shows similar completeness levels to that in the authoritative region of SCSN. We argue that the current M c of Japan is due to the success of network modernization over time. Particularly, we show that the spatiotemporal change of M c closely matches the addition of the Hi-net borehole stations to enhancing seismic-station density; it started in October 1997 in southwestern Japan, continuing to northeastern Japan until 2002. As suggested from this matching, we confirm that M c inversely correlates with station density. Further, we find that irrespective of the network change after 1997, this correlation is unchanged in time, demonstrating that the influence on M c from factors beyond station density does not vary in time. Contrary to Alaska and California (Wiemer and Wyss, 2000), our results do not attribute such factors simply to anthropogenic noise. Because this is due to the borehole stations that reduce ambient noise, we conclude that in Japan the anthropogenic noise has an insignificant effect on M c .

Natural infection with canine distemper virus in a Japanese monkey (Macaca fuscata)

A case of encephalitis in a Japanese monkey (Macaca fuscata) was examined histopathologically and serologically. The animal had brain lesions consisting of perivascular cuffs, malacia, inclusion bodies and giant cells. Monoclonal antibody to the nucleoprotein of canine distemper virus (CDV) stained the inclusions, and the distribution of the virus antigen was closely associated with that of the histological lesions. Serologically, all the 22 monkeys in the same group as the diseased monkey had relatively high titers of neutralizing antibody to CDV, but not to measles virus (MV). The pattern of the antibody titers to CDV and MV closely resembled that of cynomolgus monkeys experimentally inoculated with CDV, but differed from that of monkeys inoculated with MV. These findings suggest that an epidemic of CDV occurred in these Japanese monkeys, associated with one case of fatal viral encephalitis. This is believed to be the first report of a natural infection by CDV in non-human primates.

CSEP Testing Center and the first results of the earthquake forecast testing experiment in Japan

Major objectives of the Japanese earthquake prediction research program for the period 2009–2013 are to create earthquake forecasting models and begin the prospective testing of these models against recorded seismicity. For this purpose, the Earthquake Research Institute of the University of Tokyo has joined an international partnership to create a Collaboratory for the Study of Earthquake Predictability (CSEP). Here, we describe a new infrastructure for developing and evaluating forecasting models—the CSEP Japan Testing Center—as well as some preliminary testing results. On 1 November 2009, the Testing Center started a prospective and competitive earthquake predictability experiment using the seismically active and well-instrumented region of Japan as a natural laboratory.

BMIR-J2: a test collection for evaluation of Japanese information retrieval systems

BMIR-J2 is the first complete test collection generally available for evaluating Japanese information retrieval systems. BMIR-J2 features include a novel division of search requests based on various functions required to perform successful retrieval. BMIR-J2 and its smaller predecessor BMIR-J1 were constructed by a volunteer-based working group under the Information Processing Society of Japan. We hope that BMIR-J2 will come into wide use and that it will foster the development of Japanese IR systems.

Molecular analysis of structural protein genes of the yamagata-1 strain of defective subacute sclerosing panencephalitis virus. II. Nucleotide sequence of a cDNA corresponding to the P plus M dicistronic mRNA

The nucleotide sequence of a cloned cDNA corresponding to the P+M dicistronic mRNA of a subacute sclerosing panencephalitis (SSPE) virus was determined and compared with data of measles virus (MV). The dicistronic mRNA of the SSPE virus consisted of the 3′ proximal 626 nucleotides of P mRNA, intercistronic trinucleotides, a full length of M mRNA, and 75 poly A nucleotides. The part encoding the P protein had a high homology to MV, except at the noncoding region. The terminating consensus sequence of the P gene and the intercistronic trinucleotides of the SSPE virus were CTAC(A)6 and CCT; in MV they are TTAT(A)6 and CTT, respectively. In the M gene, the starting consensus sequence was exactly the same as MV, but at the 5′ proximal end, one third of this gene was different: The first ATG codon of the MV M gene signaling opening of the reading frame was changed to ACG in the SSPE virus and one long open reading frame started from the third ATG codon. The stop codon (TAG) of the MV M gene was also changed to CAG in the SSPE virus. Thus, the deduced SSPE-virus M protein lacked 50 amino acids at the amino terminal and had 15 extra amino acids at the carboxyl end when compared with the MV M protein.

Lessons from BMIR-J2: a test collection for Japanese IR systems

BMIR-JP is the lirat complete Japanese test collection available for use in evaluating information retrieval systems. It contains sixty queries and the IDS of 5080 newspaper articles in the fields of economics and engineering. The queries are classified into five categories, based on the functions the system is likely to use to interpret them correctly and retrieve relevant texts. This collection has two levels of relevance, topically relevant and partially relevant. Also discussed are design issues such as collection types and size. This collection and the principles derived in designing it should be helpful in the future development of new test collections.

Testing the Coulomb stress triggering hypothesis for three recent megathrust earthquakes

We test the static Coulomb stress triggering hypothesis for three recent megathrust earthquakes (the 2004 Sumatra–Andaman earthquake, the 2010 Maule earthquake, and the 2011 Tohoku-Oki earthquake) using focal mechanism solutions for actual earthquakes as receiver faults to calculate Coulomb stress changes. For the 2004 Sumatra–Andaman and 2011 Tohoku-Oki earthquakes, the median values of the Coulomb stress changes for 100 consecutive earthquakes revealed temporal changes from approximately zero before the megathrust earthquake to significant positive values following the mainshock, followed by decay over time. Furthermore, the ratio of the number of positively to negatively stressed receiver faults increased after the megathrust. These results support the triggering hypothesis that the static stress changes imparted by megathrust earthquakes cause seismicity changes. This is in contrast to the results of a previous study that used optimally orientated receiver faults to calculate Coulomb stress changes, and this difference indicates the importance of considering the spatial and temporal heterogeneities of receiver fault distributions. For the 2010 Maule earthquake, however, the results are strongly dependent on fault-slip models. Since most receiver faults are concentrated in the mainshock source region, slip models significantly affect the computed Coulomb stress changes and sometimes cause anomalous stress concentrations along the edge of each sub-fault.

Exploring Magnitude Forecasting of the Next Earthquake

Almost all forecasting of the magnitude of the next earthquake has assumed the same independent probability distribution, such as the Gutenberg–Richter law, with the same b-value (b = 0.9 in Japan region standard), throughout an earthquake sequence. Identifying a broadened forecasting procedure for general models of space-time magnitude sequences may enhance the information gain of earthquake forecasts. This manuscript explores and evaluates three such models for earthquake magnitude forecasting. The first model forecasts magnitudes by location-dependent b-values; the second model forecasts magnitudes by space-time weighted moving average of the short-term past and neighboring magnitude sequence; and the third forecasts based on short-term tightness of clustering among earthquakes. The forecasting performances of these models estimated in a learning periods are shown at each time in the CSEP Japan testing period, from November 1, 2008 till October 31, 2017. Except for the last example, the forecasts do not outperform the baseline G–R law with the b value of 0.9. We discuss the reasons by some residual analysis.

A Focal Mechanism Solution Catalog of Earthquakes (M≥2.0) in and around the Japanese Islands for 1985–1998

Abstract We determined focal mechanism solutions for 14,544 earthquakes that occurred in and around the Japanese Islands from July 1985 to December 1998 using first‐motion polarities reported by the Japan University Seismic Network and compiled by the Japan University Seismic Network Earthquake Catalog of First‐Motion Focal Mechanisms (JUNEC FM ∧ 2). This catalog covers small‐magnitude earthquakes ( M ≥2.0) prior to the recent development of seismic observation networks and automated waveform data processing systems. This catalog will prove helpful in understanding the spatial and temporal heterogeneities of stress fields by combining recent focal mechanism solutions and also will be useful for statistical analyses. Online Material: Figures of velocity structure, focal mechanisms, magnitude–frequency distributions, and temporal changes in station locations.