Expedition Menu
1. Introduction
The Question
3. Funding
4. Study Area
5. Background
Seismogenic Zone
7. Chief Scientists
8. The Journey
9. Ship Tour
10. Leaving Port
11. Seismic Method
12. Seismic Source
13. Seismic Recording
14. 3-D Acquisition
15. Life at Sea
16. In the Lab
17. Time to Depart
18. Data Processing
19. The 3-D Volume
20. Interpretation
21. Your Turn
22. Comparison
23, Publication
24. IODP Drilling

NSF Logo
This material is based
upon work supported
by the
National Science Foundation
Grant No. 0633234



NanTroSEIZE in 3-D

Imaging an Active Plate Boundary Fault
4. Nankai Tough - Study Area

Integrarted Ocean Drilling Logo
Map Showing Study Area
Location of Our Study

Our study area is located along a deep-sea trench, known as the Nankai Trough, which extends along the offshore region of southeastern Japan, near the major economic centers of Osaka and Tokyo. The blue areas in the map at the left mark the seafloor with the darker areas respresenting deep water, more than 4000 meters deep. The islands of Japan, composed on many active, sometimes explosive, volcanoes that form part of the Ring of Fire around the Pacific Rim, are shown in green. The area of our survey is outlined by the red rectangle.

Major Earthquakes and Tsunamis in Region - 1944 and 1946

On December 7, 1944 a magnitude 8.0-8.3 earthquake occurred in this area, which caused 998 deaths. The epicenter, or surface projection of the earthquake is shown by the green star and the estimated area of fault rupture, is colored in red in the map at the lower left (Tanioka, 2002) . More than 73,000 houses were destroyed or heavily damaged by the earthquake and an additional 3,000 houses were washed away by the tsunami. The quake was felt from northern Honshu to Kyushu. A large tsunami struck the Pacific Coast of Japan from Choshi, Honshu to Tosashimizu, Shikoku. Maximum wave heights of up to 8 m (26 ft) were observed on the east coast of the Kii Peninsula, Honshu. A 0.5-m tsunami was recorded on Attu, Alaska and a small tsunami was recorded at San Diego and Terminal Island, California.
Modified from http://earthquake.usgs.gov/regional/world/events/1944_12_07.php

A second undersea earthquake, with a magnitude of 8.1 to 8.4, struck this area two years later on December 20, 1946, resulting in 1,362 deaths. More than 2,600 people were injured and 100 missing: over 36,000 houses were destroyed or severely damaged in southern Honshu and on Shikoku, resulting in a half a million left homeless. An additional 2,100 houses were washed away by a tsunami, which reached heights of 5-6 m (16-20 ft) on the east coast of the Kii Peninsula, Honshu and on the east and south coasts of Shikoku. The quake was felt from northern Honshu to Kyushu. The earthquake was centered only 27 miles south of Honshu’s Kii Peninsula, shown by the green star in the map at the left. (http://earthquake.usgs.gov/regional/world/events/1946_12_20.php)

The tremor caused some buildings on Honshu to collapse, including some housing being used by U.S. occupation forces. Even worse, three major tsunamis headed toward Honshu and the smaller islands of Kyushu and Shikoku. Local geographic features determined how intense the waves were when they hit land and how much damage they caused. In some places, the water receded severely first, providing a warning to local residents who were familiar with the signs of an imminent tsunami. When the tsunami hit Honshu, 20-foot waves obliterated buildings from shorelines and about 2,000 ships were capsized as they were thrown around by the mass of water. In all, 60,000 square miles were flooded by the waves and 40,000 homes were completely destroyed.

Clearly, this region has a well-documented history of destructive earthquakes and tsunamis, which pose a hazard to Japan and many countries around the Pacific Rim. Great earthquakes occur along the Nankai Trough at an interval of about every 120 years (Ishibashi and Satake, 1998). Moreover, earthquakes of this magnitude in the future would result in death and destruction in Osaka, Kobe, and Tokyo, thereby sending shock waves throughout the global economy.

Consequently, a major international effort, called NanTroSEIZE, is underway to study this region to better understand the mechanics and properties of the fault zones that ruptured during these past events and to deploy instruments under the sea that foretell future tremors.

Map of Study Area from IODP NanTroSEIZE Overview Brochure

Rupture Areas of 1944 and 1946 earthquakes
Areas of fault rupture along the Nankai Trough
in 1944 and 1946 Earthquakes
(Modified from H. Tobin)

©Copyright 2009
July 23, 2009

Send Comments to Don Reed

Department of Geology
San Jose State University
NanTroSEIZE Drilling Objectives
Modified from IODP Nankai Trough Seismogenic Zone Experiment

What is the geologic framework of this region and why does it spawn such devastating earthquakes and tsunamis?