scholarly journals Great Earthquakes along the Nankai Trough-A New Idea for Their Rupture Mode and Time Series-

2012 ◽  
Vol 64 (2) ◽  
pp. 97-116 ◽  
Author(s):  
Tetsuzo SENO
Keyword(s):  
Time Series ◽  
Nankai Trough ◽  
Great Earthquakes ◽  
Rupture Mode

scholarly journals Amplification of tsunami heights by delayed rupture of great earthquakes along the Nankai trough

2010 ◽  
Vol 62 (4) ◽  
pp. 427-432 ◽  
Author(s):  
Kentaro Imai ◽  
Kenji Satake ◽  
Takashi Furumura
Keyword(s):  
Nankai Trough ◽  
Great Earthquakes ◽  
Delayed Rupture

Tsunami scenarios for megathrust earthquakes: mechanics of multi-segment ruptures and elastic-fluid dynamics of wave propagation

2020 ◽  
Author(s):  
Tatsuhiko Saito ◽  
Akemi Noda
Keyword(s):  
Fluid Dynamics ◽  
Strain Energy ◽  
Seismic Waves ◽  
Nankai Trough ◽  
Ocean Bottom ◽  
Bottom Pressure ◽  
Ocean Bottom Pressure ◽  
Megathrust Earthquakes ◽  
Great Earthquakes ◽  
Pressure Changes

<p>Great earthquakes repeatedly occurred with different rupture processes in the Nankai trough, southwestern Japan. The 1944 Tonankai and the 1946 Nankai earthquakes (M ~8) caused serious tsunami damage over many areas along the coastline. The greatest earthquake in this region is the 1707 Hoei earthquake (M 8.4) that is believed to have ruptured the whole region (~600 km) of the Nankai Trough. The purpose of this study is to theoretically assess the tsunami height along the coasts excited by great earthquakes that can possibly occur in future in this region and simulate observable tsunami records during the earthquakes.</p><p>This study employed a new method for making various rupture scenarios. Based on a shear-stress distribution along the plate boundary estimated by the GNSS data analyses (Noda et al. 2018 JGR), we calculated coseismic slip distributions to release the accumulated stress for possible multi-segment rupture scenarios. Then, we used the strain energy released by the rupture to evaluate the possibility of each event. The released strain energy should be larger than the energy dissipated on the fault. However, for some scenarios, the released strain energy was smaller than the dissipated energy under the assumptions of friction laws. Such rupture scenarios are not likely to occur in the viewpoint of earthquake mechanics. This approach can provide necessary conditions of the strain energy or the accumulated stress levels for multi-segment rupture processes, while methods based on empirical or kinematic approaches do not treat stress or interseimsmic stress-accumulation periods required for ruptures.</p><p>Another distinctive point in our approach is that we theoretically synthesize ocean-bottom pressure changes caused by both seismic waves and tsunamis using a simulation method based on elastic and fluid dynamics (Saito and Tsushima 2016 JGR; Saito et al. 2019 Tectonophysics). Seismic wave contributions to ocean-bottom pressure changes are critically important for the synthetics in near-field or inside rupture areas because the seismic waves overlap with tsunami signals and work as noise for real-time tsunami monitoring. The records simulated in this study can be used to examine the monitoring ability of a deep-ocean observation network for megathrust earthquakes and tsunamis in this region.</p>

Fatigue Evaluation of Drill Pipes for Scientific Drilling Program by Applying Non-Stop Driller Concept

2019 ◽  
Author(s):  
Tomoya Inoue ◽  
Masahiko Fujikubo ◽  
Kenji Nakano ◽  
Noriaki Sakurai
Keyword(s):  
Time Series ◽  
Fatigue Strength ◽  
Nankai Trough ◽  
Drilling Fluid ◽  
Drill Pipe ◽  
Ship Motions ◽  
Bending Stress ◽  
Deep Drilling ◽  
Scientific Drilling ◽  
Drilling Equipment

Abstract The scientific drilling vessel Chikyu is performing Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE), a challenging deep drilling activity, for scientific purpose. We faced difficulty to drill deep during past NanTroSEIZE operations due to unstable sediments and insufficient cutting removal. Non-Stop Driller concept is, therefore, applied for the operation of NanTroSEIZE scheduled to start Oct. 2018 to enable continuous circulation of drilling fluid circulation. The Non-Stop Driller concept requires an additional, specially-designed sub called an “NSD sub” with a ball valve for drilling fluid inlet. Generally, the fatigue strength of a drill pipe is a critical factor governing the performance of challenging deep drilling. This study, therefore, focused on the fatigue failure of the NSD sub due to the bending stress caused by interference with risers including flex joints, ship structure, or drilling equipment resulting from ship motions. The bending stress leads to cyclic stress caused by rotation of the drill pipe. This is especially the case at the Nankai Trough where ocean currents are very strong reaching or sometimes exceeding 4 knots, a high bending stress is assumed to be exerted on the NSD sub. Full-scale fatigue tests of the NSD sub were first conducted to acquire the actual fatigue curve. Further, the bending stress distribution of a drill pipe, which refers to the locus of the bending stress during the drilling operation, was analyzed by considering interference of the drill string with the structure, drilling equipment, and risers that are deformed by the ocean current. Time-series ship motions is prepared using the response amplitude operators of the Chikyu for the sea states at Nankai Trough area, and then time-series stress response is obtained by considering the operational conditions such as rate of penetration and rotational velocity of drill pipe. The numbers of occurrence of each stress amplitude can be counted from the time-series stress response. Consequently, the cumulative damage ratio is calculated for evaluating the fatigue of the NSD sub. The results confirmed that the cumulative fatigue is within a safe range. This study focused on the evaluation of the fatigue strength of the specially designed NSD sub for the challenging scientific drilling operation at Nankai Trough, a harsh environment because of the presence of strong ocean currents. This paper presents the overview of NanTroSEIZE including the Non-Stop Driller concept, and the results of fatigue evaluations.

Seismic characteristics around the fault segment boundary of historical great earthquakes along the Nankai Trough revealed by repeated long-term OBS observations

2010 ◽  
Vol 37 (9) ◽  
pp. n/a-n/a ◽  
Author(s):  
Kimihiro Mochizuki ◽  
Kazuo Nakahigashi ◽  
Asako Kuwano ◽  
Tomoaki Yamada ◽  
Masanao Shinohara ◽  
...  
Keyword(s):  
Nankai Trough ◽  
Fault Segment ◽  
Segment Boundary ◽  
Great Earthquakes ◽  
Seismic Characteristics
Sign in / Sign up

Export Citation Format

Share Document