Upper boundaries of the Pacific and Philippine Sea plates near the triple junction off the Boso Peninsula deduced from ocean-bottom seismic observations
© The Author(s) 2017
Received: 15 October 2016
Accepted: 20 January 2017
Published: 9 February 2017
KeywordsBoso Peninsula Ocean-bottom seismometer Philippine Sea plate Pacific plate Hypocenter distribution
The region is characterized by various seismic and geodetic activities (Fig. 1a): The 1703 Genroku Kanto earthquake (M = 7.9–8.2) and the 1923 Kanto earthquake (M w = 7.9) were interplate events associated with the subduction of the PHS (e.g., Matsu’ura et al. 2007; Namegaya et al. 2011; Sato et al. 2016). Slow slip events occur with an average interval of 6 years near the rupture area of these interplate earthquakes (e.g., Ozawa et al. 2003; Sagiya 2004; Hirose et al. 2014). Significant increases in seismicity and Coulomb stress after the 2011 Tohoku-Oki earthquake (M = 9) are also recognized in the region (Toda et al. 2011).
To understand these seismic and geodetic phenomena, it is important to accurately determine the geometry of the boundaries between the three plates, and the plate boundaries in the region off the Boso Peninsula have been studied extensively. Uchida et al. (2010) determined the upper boundary of the PHS by analyzing repeating earthquakes and seismic waves converted at the plate boundary. Their results showed that the upper boundary of the PHS is located at depths of 10–30 km beneath the Boso Peninsula. The upper boundary of the subducted PAC has been detected at depths greater than 40 km based on relocated hypocenter distributions (Nakajima and Hasegawa 2006; Nakajima et al. 2009). The upper boundary at shallower depths has not yet been well constrained, but has been estimated through interpolation from the location of the PAC upper boundary at a depth of 40 km and the trench axis. Because previous studies mainly used data from land-based stations alone, the shallow parts of the PAC–NA and PHS–NA boundaries beneath the area offshore of the Boso Peninsula (particularly trenchward from 141°E) have not yet been defined. Precise rendering of the plate boundaries, particularly at shallow depths, is also crucial for assessing the seismic and tsunami hazards of large interplate earthquakes. The 2011 Tohoku-Oki earthquake indicated that the shallowest part of the subducted Pacific slab has the potential for significant seismic slip (e.g., Yagi and Fukahata 2011; Satake et al. 2013).
Few seismic observations have been conducted with ocean-bottom seismometers (OBS) off the Boso Peninsula, particularly south of 35.5°N. The Earthquake Research Institute (ERI) of the University of Tokyo conducted aftershock observations following the 2011 Tohoku-Oki earthquake across a broad area of the Japan Trench forearc region (Shinohara et al. 2011, 2012a), but they did not cover the majority of the region off the Boso Peninsula (south of 35.5°N). In this study, we determine hypocenter distributions and focal mechanisms of earthquakes off the Boso Peninsula, as close to the Japan Trench and Sagami Trough as possible, by using data from both OBSs and land-based stations.
Specifications of the stations used in this study. Stations in italic were deployed for seafloor observation
Natural frequency of sensor (Hz)
Sampling frequency (Hz)
Number of stations
Mar. 2012–Mar. 2013
Mar. 2012–Mar. 2013
May 2012–Mar. 2013
Dec. 2012–Mar. 2013
Oct. 2011–Aug. 2012
1, 3, 5
We analyzed approximately 1000 earthquakes between March 2012 and March 2013 from the Japan Meteorological Agency (JMA) catalog (Fig. 1b, https://hinetwww11.bosai.go.jp/auth/?LANG=en), with magnitudes ranging from 1.1 to 6.3. To select earthquakes, we delineated three regions (indicated by orange, yellow, and blue lines in Fig. 1b) where we expected the hypocenters to be well constrained by data from JAMSTEC and ERI OBSs, and land-based stations. Of the earthquakes in the JMA catalog located within these three regions, we selected those with signals that were recorded by at least three JAMSTEC OBS stations. We picked the onset times of P- and S-wave arrivals manually from the vertical and horizontal components of the OBS data. We also recorded the polarity of P-wave first motions when possible. We used the DPG records of one BBOBS to obtain onset times and first motions in cases where velocity seismograms were not available. For the land-based stations, we collected P- and S-wave arrival data and P-wave first motion data from the catalog published by NIED. The total numbers of P- and S-wave arrivals used in this study were 23,670 and 12,872, respectively.
Tsuru et al. (2002) established the lateral variation of sedimentary layers along the Japan Trench forearc regions based on reflection studies; the thicknesses of sedimentary layers would also be expected to vary between the OBS sites. To account for the heterogeneity of sediment layers, we introduce a station correction term for earthquake location determination. We iteratively located earthquakes using the average difference between observed and calculated travel times (O–C times) at each station as the station correction until the root-mean-squares (RMS) of the O–C times converged.
Next, we estimated hypocenter locations using a simplified three-dimensional velocity model (Fig. 2b), applying the three-dimensional geometries of the subducted PAC obtained in previous studies (Nakajima and Hasegawa 2006; Nakajima et al. 2009) based on interplate earthquake distribution (Fig. 1a). The oceanic crust model for the PAC was constructed from the results of a previous refraction study along the Japan Trench (Ito et al. 2005). We assumed a 5-km-thick layer of V p = 7.9 km/s just below the oceanic crust of the PAC (Ito et al. 2005). For the deeper part of the PAC mantle, we assumed a V p of 8.35 km/s based on results of tomographic study near the Boso Peninsula (Nakajima et al. 2009). The overlying crust and mantle consist of the NA and PHS plates, and we assumed crustal V p to be 5.5 km/s, which is an average velocity above the Moho based on results of a refraction study off the Boso Peninsula (Nakahigashi et al. 2012). The boundary between the crust and mantle was assumed to remain at a constant depth of 20 km, as described by Nakahigashi et al. (2012). A tomographic study from Nakajima et al. (2009) was used to derive the NA mantle V p of 7.2 km/s. To construct the S-wave velocity model, we assumed a V p/V s ratio of 1.73 in the crust and 1.78 in the mantle based on the studies of Nakajima et al. (2009) and Hino et al. (2009).
We used NonLinLoc software (Lomax et al. 2000) based on a grid-search algorithm for hypocenter determination with a three-dimensional model. The grid node spacing of the velocity model was assumed to be 1 km. We introduced site correction values calculated from average O–C times in the same manner as that used for hypocenter determination with the one-dimensional velocity model.
After the hypocenters were located, we determined focal mechanisms based on P-wave polarity data using the FOCMEC software (Snoke 2003) for earthquakes with at least seven available polarity data.
Figure 3b shows the hypocenter distribution based on the three-dimensional velocity model, which is less scattered and more compact than that based on the one-dimensional velocity model. We located 881 earthquakes with an error of less than 2 km in the horizontal direction and less than 3 km in the depth direction and an RMS of the travel time residual below 1 s. The average errors in epicenters and focal depths were 0.70 and 0.75 km, respectively. The RMS of travel time residuals for P-wave and S-wave arrival times were 0.33 and 0.73 s, respectively. Because the RMS of travel time residuals based on the three-dimensional model are smaller than those based on the JMA2001 model, we used hypocenter locations derived from the three-dimensional model in further analysis.
We obtained focal mechanism solutions for 219 of 881 earthquakes based on the three-dimensional model. According to the JMA catalog, the magnitudes of these earthquakes range from 2.0 to 6.3. These earthquakes have errors in epicenter and focal depth location of less than 1.3 km and less than 2.2 km, respectively. We selected mechanism solutions with less than or equal to three inconsistent polarity data. The number of inconsistent data was ≤1 for 159 of the 219 total solutions. For the solutions with two or three inconsistent polarity data, the inconsistent data accounted for 12% of the total, on average. We provide examples of the focal mechanisms with the distribution of polarity data in Additional file 2: Figure A2. Because the coverage of the polarity data on the focal sphere is generally good, the focal mechanisms determined in the present study are considered to be robust. We also show the frequency distributions of azimuthal coverage and take-off angle coverage in Additional file 3: Figure A3. Azimuthal coverage ranged from 171.4° to 358.3°, and take-off angle coverage ranged from 9.3° to 77.2°.
Following the criteria of Frohlich (1992), the focal mechanisms of 100 earthquakes were classified as normal faulting, 77 as reverse faulting, and 29 as strike-slip faulting. We plotted the distributions of these focal mechanisms for the shallow and PAC groups in Figs. 4 and 5, respectively, along with a vertical section parallel to the PAC subduction direction. Only the focal mechanisms of earthquakes with magnitudes greater than 2.3 are plotted in the figures, to enhance their visibility, but the same pattern is shown when earthquakes with magnitudes between 2.0 and 2.3 are included.
For the shallow group, more than half of the focal mechanisms were normal faulting. Normal and strike-slip faulting earthquakes are distributed throughout the NA crust, whereas reverse-faulting earthquakes typically occur only at depths greater than 10 km. Most reverse-faulting earthquakes are located east of 141°. The PAC group is dominated by reverse faulting and shows fewer normal and strike-slip faulting earthquakes. Reverse-faulting earthquakes are also detected close to the trench–trench–trench triple junction.
Comparison of hypocenter distribution and crustal structure
Upper boundary of the PAC
The low-angle thrust-faulting earthquakes have hypocenters as shallow as 10–15 km in the off-Ibaraki region (north of 36°N). Here, Shinohara et al. (2012a) identified interplate earthquake depths shallower than 40 km at the upper boundary of the PAC using seismic observations with OBSs. Mochizuki et al. (2008) determined the detailed configuration of the upper boundary of the PAC with refraction surveys along paths indicated by the yellow lines in Fig. 7a and estimated the depths of the upper boundaries of the PAC to be 8–15 km. These depths are nearly consistent with the focal depths of the low-angle thrust-faulting earthquakes determined in this study (Fig. 7b). In addition, for the first time, we have located low-angle thrust-faulting earthquakes along the upper boundary of the PAC off the Boso Peninsula (south of 36°) to depths of up to 14 km (Fig. 7c). At depths greater than 40 km, the focal depths of low-angle thrust-faulting earthquakes are consistent with the location of the upper boundary of the PAC determined by previous studies (Nakajima and Hasegawa 2006; Nakajima et al. 2009).
The upper boundary of the PHS
To locate the upper boundary of the PHS, we analyzed 16 low-angle thrust-faulting earthquakes determined from the shallow group. The focal mechanisms are plotted along profiles parallel to the PAC subduction direction (Fig. 7c) and parallel to the PHS subduction direction (Fig. 7d). Most were located near the bottom of the shallow group (see Figs. 4d, 7c). Eleven of the earthquakes had focal mechanisms with a slip direction parallel to the direction of PHS subduction (NW‒SE), and one earthquake had a dip direction parallel to the PHS (N‒S). Low-angle thrust-faulting earthquakes occur near the PHS–NA boundary identified by Nakahigashi et al. (2012), which is also plotted in Fig. 7c, d. If these earthquakes are assumed to represent slip along the upper boundary of the PHS, the boundary off the Boso Peninsula is approximately 6 km shallower than previously delineated (Uchida et al. 2010), in the area between 34.8–35.5°N and 140.9–141.6°E (red solid curve in Fig. 7d). The shift of the PHS upper boundary arises mainly because the focal depths determined using OBS data were shallower than those derived from land-based data alone (Fig. 3). To connect the upper boundary of the PHS in the trenchward area determined in this study to that in the landward area identified by Uchida et al. (2010), the tip of the PHS must bend upward at longitudes around 140.9–141.3°E (red broken curve in Fig. 7d), which was also proposed by Uchida et al. (2010) based on their converted wave analysis.
We compared the focal mechanisms determined in this study with centroid moment tensor (CMT) solutions of 20 earthquakes for which both the CMT solutions and mechanism solutions (obtained in this study) were available (Additional file 4: Figure A4). The CMT solutions were determined through waveform inversion using F-net data (http://www.fnet.bosai.go.jp/top.php?LANG=en). The 20 earthquakes had magnitudes greater than 3.5, and the variance reductions of the waveform inversion were greater than 50%. The average difference in the dip angle of focal mechanisms between the F-net data and the results of this study is 19.6° with a standard deviation of 11.0°, and the average difference in strike angle is 28.0° with a standard deviation of 30.5°. Considering the differences in data and methods (waveform inversion for the CMT solutions versus the P-wave first motion method), we consider the focal mechanisms determined in this study to be consistent with the CMT solutions. Comparison of focal mechanisms for three of the 20 earthquakes with those reported in the Global CMT catalog (http://www.globalcmt.org) (Dziewonski et al. 1981; Ekström et al. 2012) shows that the focal mechanisms given by the F-net, Global CMT, and this study are mutually consistent.
We have observed a significant number of normal and strike-slip faulting earthquakes (Figs. 4, 5), and most have T-axes in an almost E–W direction. In NA crust, significant enhancement of trench-normal extensional stress after the 2011 Tohoku-Oki earthquake was reported over a broad area in the forearc region by Hasegawa et al. (2012). The vigorous shallow seismicity with E–W extensional focal mechanisms we report here is consistent with the post-2011 seismic change. Asano et al. (2011) reported an increase of extensional seismicity within the subducting PAC slab near the large coseismic slip zone of the 2011 earthquake. The normal and strike-slip faulting events among the PAC group are interpreted as intraslab earthquakes, and their focal mechanisms suggest significant change of stress field off the Boso Peninsula, although the region is distant from the main rupture of the 2011 earthquake.
The focal depths of relocated hypocenters determined using OBS data are generally shallower than those determined by JMA in the study area.
Hypocenter distributions can be separated into two groups; one group is shallower than the upper boundaries of the PAC, and the other follows the upper boundary of the PAC.
Both the hypocenter distributions and the focal depths of low-angle thrust-faulting earthquakes are consistent with the NA–PAC and NA–PHS plate boundaries, which were determined by a previous refraction study off the Boso Peninsula (Nakahigashi et al. 2012).
Low-angle thrust-faulting earthquakes shallower than 40 km at the upper boundary of the PAC are detected for the first time in the off-Boso Peninsula region.
More than half of the low-angle thrust-faulting earthquakes in the shallow group have a slip direction parallel to the direction of PHS subduction. If these events are assumed to represent the upper boundary of the PHS, the depth of this boundary off the Boso Peninsula is approximately 6 km shallower than previously determined using only land-based data from the area between 34.8–35.5°N and 140.9–141.6°E.
North American plate
Philippine Sea plate
Earthquake Research Institute
broadband ocean-bottom seismometer
short-period ocean-bottom seismometer
Japan Agency of Marine-Earth Science and Technology
differential pressure gauge
National Research Institute for Earth Science and Disaster Prevention
Japan Meteorological Agency
- O–C times:
observed and calculated travel times
centroid moment tensor
- V p :
- V s :
AI performed the BBOBS observations, data processing and analysis and wrote the manuscript. HS also performed the BBOBS observations, and KO performed the SPOBS observations. DS and RH suggested improvements of the manuscript. KN and MS provided support for the OBSs data collection by ERI. MN and YY supported the data processing and analysis. All authors read and approved the final manuscript.
This study was partly supported by the Special Coordination Funds for the Promotion of Science and Technology (MEXT, Japan) designated as integrated research for the 2011 Tohoku Earthquake off the Pacific coast. We used data obtained from the Hi-net and F-net systems operated by NIED, and onshore observations obtained by JMA. Tsutomu Takahashi performed initial SPOBS data processing. We thank Naoki Uchida for providing a list of repeating earthquakes. The editor Junich Nakajima and an anonymous reviewer helped to greatly improve the manuscript.
The authors declare that they have no competing interests.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
- Araki E, Sugioka H (2009) Calibration of deep sea differential pressure gauge. JAMSTEC-R 9:141–148 (in Japanese with English abstract) View ArticleGoogle Scholar
- Asano Y, Saito T, Ito Y, Shiomi K, Hirose H, Matsumoto T, Aoi S, Hori S, Sekiguchi S (2011) Spatial distribution and focal mechanisms of aftershocks of the 2011 off the Pacific coast of Tohoku Earthquake. Earth Planets Space 63:669–673. doi:10.5047/eps.2011.06.016 View ArticleGoogle Scholar
- DeMets C, Gordon RG, Argus DF (2010) Geologically current plate motions. Geophys J Inter. doi:10.1111/j.1365-246X.2009.04491.x Google Scholar
- Dziewonski AM, Chou TA, Woodhouse JH (1981) Determination of earthquake source parameters from waveform data for studies of global and regional seismicity. J Geophys Res 86:2825–2852. doi:10.1029/JB086iB04p02825 View ArticleGoogle Scholar
- Ekström G, Nettles M, Dziewonski AM (2012) The global CMT project 2004–2010: centroid-moment tensors for 13,017 earthquakes. Phys Earth Planet Inter 200–201:1–9. doi:10.1016/j.pepi.2012.04.002 View ArticleGoogle Scholar
- Frohlich C (1992) Triangle diagrams: ternary graphs to display similarity and diversity of earthquake focal mechanisms. Phys Earth Planet Inter 75:93–198View ArticleGoogle Scholar
- Hasegawa A, Yoshida K, Asano Y, Okada T, Iinuma T, Ito Y (2012) Change in stress field after the 2011 great Tohoku-Oki earthquake. Earth Planet Sci Lett 355–356:231–243. doi:10.1016/j.epsl.2012.08.042 View ArticleGoogle Scholar
- Hino R, Azuma R, Ito Y, Yamamoto Y, Suzuki K, Tsushima H, Suzuki S, Miyashita M, Tomori T, Arizono M, Tange G (2009) Insight into complex rupturing of the immature bending normal fault in the outer slope of the Japan Trench from aftershocks of the 2005 Sanriku earthquake (Mw = 7.0) located by ocean bottom seismometry. Geochem Geophys Geosyst 10:Q07O18 doi:10.1029/2009GC002415
- Hirata N, Matsu’ura M (1987) Maximum-likelihood estimation of hypocenter with origin time eliminated using nonlinear inversion technique. Phys Earth Plant Inter 47:50–61View ArticleGoogle Scholar
- Hirata N, Narumi T, Amishiki T, Katao H, Kaiho Y, Kashiwara S, Hino R, Baba H, Shiobara H, Koresawa S, Shinohara M, Kubo A, Kanazawa T, Kasahara J, Kinoshita H (1992) Report on DELP 1989 Cruise in the TTT junction areas Part 2: upper crustal structure near the trench–trench–trench triple junction off Boso Peninsula, Japan. Bull Earthq Res Inst Univ Tokyo 67:479–512Google Scholar
- Hirose H, Matsuzawa T, Kimura T, Kimura H (2014) The Boso slow slip events in 2007 and 2011 as a driving process for the accompanying earthquake swarm. Geophys Res Lett 41:2778–2785. doi:10.1002/2014GL059791 View ArticleGoogle Scholar
- Hori S (2006) Seismic activity associated with the subducting motion of the Philippine Sea plate beneath the Kanto district, Japan. Tectonophysics 417:85–100. doi:10.1016/j.tecto.2005.08.027 View ArticleGoogle Scholar
- Igarashi T, Matsuzawa T, Hasegawa A (2003) Repeating earthquakes and interplate aseismic slip in the northeastern Japan subduction zone. J Geophys Res. doi:10.1029/2002JB001920 Google Scholar
- Ishida M (1992) Geometry and relative motion of the Philippine Sea plate and Pacific plate beneath the Kanto-Tokai district, Japan. J Geophys Res 97:489–513View ArticleGoogle Scholar
- Ito A, Fujie G, Miura S, Kodaira S, Kaneda Y, Hino R (2005) Bending of the subducting oceanic plate and its implication for rupture propagation of large interplate earthquakes off Miyagi, Japan, in the Japan Trench subduction zone. Geophys Res Lett 32:L05310. doi:10.1029/2004GL022307 Google Scholar
- Kanazawa T, Shinohara M, Shiobara H (2009) Recent progress in seafloor earthquake observations and instruments in Japan. Zisin 61:S55–S68 (in Japanese with English abstract) View ArticleGoogle Scholar
- Lomax A, Virieux J, Volant P, Berge C (2000) Probabilistic earthquake location in 3D and layered models: Introduction of a Metropolis-Gibbs method and comparison with linear locations. In: Thurber CH, Rabinowitz N (eds) Advances in seismic event location. Kluwer, Amsterdam, pp 101–134View ArticleGoogle Scholar
- Matsu’ura M, Noda A, Fukahata Y (2007) Geodetic data inversion based on Bayesian formulation with direct and indirect prior information. Geophys J Int 171(3):1342–1351View ArticleGoogle Scholar
- Mochizuki K, Yamada T, Shinohara M, Yamanaka Y, Kanazawa T (2008) Weak Interpolate coupling by seamounts and repeating M7 earthquakes. Science 321:1194–1197View ArticleGoogle Scholar
- Nakahigashi K, Shinohara M, Mochizuki K, Yamada T, Hino R, Sato T, Uehira K, Ito Y, Murai Y, Kanazawa T (2012) P-wave velocity structure in the southernmost source region of the 2011 Tohoku earthquakes, off the Boso Peninsula deduced by an ocean bottom seismographic survey. Earth Planets Space 64:1149–1156. doi:10.5047/eps2012.06.006 View ArticleGoogle Scholar
- Nakajima J, Hasegawa A (2006) Anomalous low-velocity zone and linear alignment of seismicity along it in the subducted Pacific slab beneath Kanto, Japan: reactivation of subducted fracture zone? Geophys Res Lett 33:L16309. doi:10.1029/2006GL026773 View ArticleGoogle Scholar
- Nakajima J, Hirose F, Hasegawa A (2009) Seismotectonics beneath the Tokyo metropolitan area, Japan: effect of slab–slab contact and overlap on seismicity. J Geophys Res 114:B08309. doi:10.1029/2008JB006101 View ArticleGoogle Scholar
- Namegaya Y, Satake K, Shishikura M (2011) Fault models of the 1703 Genroku and 1923 Taisho Kanto earthquakes inferred from coastal movements in the southern Kanto area. Ann Rep Act Fault Paleoearthq Res 11:107–120 (in Japanese with English abstract) Google Scholar
- Obana K, Kodaira S, Shinohara M, Hino R, Uehira K, Shiobara H, Nakahigashi K, Yamada T, Sugioka H, Ito A, Nakamura Y, Miura S, No T, Takahashi N (2013) Aftershocks near the updip end of the 2011 Tohoku-Oki earthquake. Earth Planet Sci Lett 382:111–116. doi:10.1016/j.epsl.2013.09.007 View ArticleGoogle Scholar
- Okada Y, Kasahara K, Hori S, Obara K, Sekiguchi S, Fujiwara H, Yamamoto A (2004) Recent progress of seismic observation networks in Japan-Hi-net, F-net, K-NET and KiK-net. Earth Planets Space 56:xv–xxviii
- Ozawa S, Miyazaki S, Hatanaka Y, Imakiire T, Kaidzu M, Murakami M (2003) Characteristic silent earthquakes in the eastern part of the Boso Peninsula, Central Japan. Geophys Res Lett. doi:10.1029/2002GL016665 Google Scholar
- Sagiya T (2004) Interplate coupling in the Kanto District, Central Japan, and the Boso Peninsula Silent Earthquake in May 1996. Pure appl Geophys 161:2327–2342. doi:10.1007/s00024-004-2566-6 View ArticleGoogle Scholar
- Satake K, Fujii Y, Harada T, Namegawa Y (2013) Time and space distribution of coseismic slip of the 2011 Tohoku earthquake as inferred from Tsunami Waveform data. Bull Seism Soc Am 203(2B):1473–1492. doi:10.1785/0120120122 View ArticleGoogle Scholar
- Sato T, Higuchi H, Miyauchi T, Endo K, Tsumura N, Ito T, Noda A, Matsu’ura M (2016) The source model and recurrence interval of Genroku-type Kanto earthquakes estimated from paleo-shoreline data. Earth Planets Space 68:17. doi:10.1186/s40623-016-0395-3 View ArticleGoogle Scholar
- Shinohara M, Yamada T, Nakahigashi K, Sakai S, Mochizuki K, Uehira K, Ito Y, Azuma R, Kaiho Y, No T, Shiobara H, Hino R, Murai Y, Yakiawra H, Sato T, Machida Y, Shinbo T, Isse T, Miyamachi H, Obana K, Takahashi N, Kodaira S, Kaneda Y, Hirata K, Yoshikawa S, Obara K, Iwasaki T, Hirata K (2011) Aftershock observation of the 2011 off the Pacific coast of Tohoku Earthquake by using ocean bottom seismometer network. Earth Planets Space 63:835–840. doi:10.5047/eps.2011.05.020 View ArticleGoogle Scholar
- Shinohara M, Machida Y, Yamada T, Nakahigashi K, Shinbo T, Mochizuki K, Murai Y, Hino R, Ito Y, Sato T, Shiobara H, Uehira K, Yakiwara H, Obana K, Takahashi N, Kodaira S, Hirata K, Tsushima H, Iwasaki T (2012a) Precise aftershock distribution of the 2011 off the Pacific coast of Tohoku Earthquake revealed by an ocean-bottom seismometer network. Earth Planets Space 64:1137–1148. doi:10.5047/eps.2012.09.003 View ArticleGoogle Scholar
- Shinohara M, Shiobara H, Suyehiro K (2012b) Site selection, preparation and installation of seismic stations. In: Bormann P (ed) New manual of seismological observatory practice 2 (NMSOP-2), Potsdam: Deutsches GeoForschungsZentrum GFZ, 7.5 Marine seismic observation of chapter 7. doi:10.2312/GFZ.NMSOP-2_ch7
- Snoke JA (2003) FOCMEC: FOcal MEChanism determinations. In: Lee WHK, Kanamori H, Jennings PC, Kisslinger C (eds) International handbook of earthquake and engineering seismology. Academic Press, San Diego, Chapter 85.12
- Toda S, Stein SR, Lin J (2011) Wide spread seismicity excitation throughout central Japan following the 2011 M = 0.9 Tohoku earthquake and its interpretation by Coulomb stress transfer. Geophys Res Lett 38:L00G03. doi:10.1029/2011GL047834 View ArticleGoogle Scholar
- Tsuru T, Park JO, Miura S, Kodaira S, Kido Y, Hayashi T (2002) Along-arc structural variation of the plate boundary at the Japan Trench margin: implication of interplate coupling. J Geophys Res 107:B12. doi:10.1029/2001JB001664 View ArticleGoogle Scholar
- Uchida N, Nakajima J, Hasegawa A, Matsuzawa T (2009) What controls interplate coupling? Evidence for abrupt change in coupling across a border between two overlying plates in the NE Japan subduction zone. Earth Planet Sci Lett 283:111–121View ArticleGoogle Scholar
- Uchida N, Matsuzawa T, Nakajima J, Hasegawa A (2010) Subduction of a wedge-shaped Philippine Sea plate beneath Kanto, central Japan, estimated from converted waves and small repeating earthquakes. J Geophys Res 115:B07309. doi:10.1029/2009JB006797 Google Scholar
- Uchida N, Asano Y, Hasegawa A (2016) Acceleration of regional plate subduction beneath Kanto Japan, after the 2011 Tohoku-oki earthquake. Geophys Res Lett. doi:10.1002/2016GL070298 Google Scholar
- Ueno H, Hatakeyama S, Aketagawa T, Funasaki J, Hamada N (2002) Improvement of hypocenter determination procedures in the Japan Meteorological Agency. Q J Seismol 65:123–134 (in Japanese with English abstract) Google Scholar
- Yagi Y, Fukahata Y (2011) Rupture process of the 2011 Tohoku-oki earthquake and absolute elastic strain release. Geophys Res Lett 38:L19307. doi:10.1029/2011GL048701 View ArticleGoogle Scholar