This page is the home for data, figures, references that are relevant to the Seismogenic Experiment (SEIZE) Initiative and the Nankai-Japan Trench focus area. If you have questions, suggestions, or if you want to submit data, please contact Andreas Aichinger at the MARGINS Office, who will be happy to try to help you.

Here are some figures related to the Nankai-Japan Trench that are of interest. Please click on the thumbnails to see the enlarged version.

Mantle wedge tomography across Honshu, Japan, after Zhao et al. (1992). Earthquake loci are projected as small open circles, relative mantle P-wave velocities are shown in colors, from red (slow) to blue (fast). Note that there are two parallel zones of earthquakes, with the upper one defining the upper part of the plate. Note that the zone of “slow” mantle, inferred to reflect partially molten zones, lie several tens of km above the subducted slab.

Effect of the subducted slab beneath Alaska on regional seismic waveforms that travel along the subducted crust (Abers and Sarker, 1996). Red circles denote earthquakes at 100-150 km depth within the slab. Seismograms recorded at COL are simple for P waves that do not travel along the slab (green arrow), but pulse dispersion characterizes waves that travel along the slab (red arrows). Inset shows structure needed to produce this effect, a layer of subducted crust, ~5% slower than surrounding mantle. Velocities are consistent with lawsonite blueschist (Helffrich, 1996) but not gabbro or eclogite.

Metamorphic facies for wet basalt, showing seismic P-wave velocities (km/s), from Peacock (1993) and Helffrich (1996). Black lines show P-T trajectories of subducting material for upper (UC) and lower (LC) crust. For comparison, mantle peridotite should have velocities of 8.0-8.2 km/s under similar conditions, and unaltered crust near 6.5 - 7.0 km/s. The seismic wave distortion measurements shown in Fig. 8a are consistent with lawsonite blueschist or with mixtures of eclogite and basalt.

Seismic Reflection Data from Nankai available via the UTIG web site

UTIG has maintained this archive since 1975 with internal funding.  Because many of the original investigations were publicly funded, the majority of these data are in the public domain.  In 1998, The National Science Foundation provided funds for the media costs associated with our transcription from Exabyte to Digital Linear Tape (DLT).  In order to make the data publicly available, and to preserve the integrity of the data over the long term, UTIG has created this database.  Currently, there are approximately 23,000 files of data, of which 3000 of the files are stacked and processed data, and the remainder being shot gathers.  The data is mostly in SEG-Y or SEG-D formats. 

Last updated August 31, 2000