Masterprosjekt vår 2019 ved GEO - Kuvvet Atakan

Project description

The largest earthquakes on Earth occur in subduction zones, the most recent examples being 2011 Japan (Mw9.0); 2012 Chile (Mw8.8); and 2004 Sumatra (Mw9.1). All of these earthquakes resulted in a large number of causalities both due to ground shaking and tsunamis. Large plate deformation occurs both before, during and after such events, and more information is needed to better understand the tectonic processes in subduction zones for earthquake risk and tsunami risk mitigation.

The focus region in this project is the Nankai Trough off the south-eastern coast of Japan, which has a history of very large and devastating earthquakes. The area from Tokyo and south is the most densely populated area of Japan, and it is exposed to a large earthquake potential. Therefore, the Japanese earthquake monitoring initiatives are extensive.

Hypothesis (scientific problem)
The rate and magnitude of seafloor deformations across subduction zones entail information on how tightly the plate boundaries are coupled in the inter-seismic (in between two large earthquakes) and co-seismic periods. This information is key to understand the fundamental processes leading up to earthquakes. DONET 1 and 2 are permanent seafloor installations for monitoring tectonic plate movement, earthquakes and tsunamis, and are developed and installed by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). These installations are cabled networks of sensors covering a moderate size area of 85 km x 200 km.

The tectonic plate movements are also monitored through the JHOD network, a sustainable seafloor geodetic observation network, which covers more sparsely a very large area of 120 km x 600 km with a total of 15 measuring stations. Here, seafloor deformation is monitored using a combination of acoustic ranging and GPS. The detection threshold is 3-4 cm/year for both horizontal and vertical deformation.

Vertical seafloor deformation monitoring as applied for hydrocarbon monitoring within the oil and gas industry has proved to provide mm accuracy even in areas with challenging oceanographic conditions. The proposed methodology is based on high accuracy seafloor pressure measurements acquired through repeat surveys, and do not require expensive permanent instrumentation at the seafloor. This opens for expanding the coverage of the existing instrumentation and provide cross- calibration of the different permanent installations. Moreover, the difference between 3-4 cm- accuracy and mm-accuracy can mean several years difference in the ability to detect changes at the seabed. Hence, this methodology may serve as an important addition to the existing infrastructure used for monitoring tectonic plate movements.

Expected work
The main objective of the thesis will be to assess the feasibility of survey-based seafloor deformation monitoring above the Nankai Trough. For this, three main tasks are identified:
• Modelling of the expected seafloor deformation from geophysical processes in the subduction zone throughout the earthquake cycle
• Study oceanographic and tidal effects in the area of interest
• Estimation of the expected and required accuracy of vertical seafloor deformation measurements within the new application

Prerequisites 

None, but the student should have some mathematical background and interest.

Eksterne data? / External data?
Earthquake data and GPS-velocities from ISC, USGS, JMA, NIED; detailed bathymetry data, oceanographic information, and interpreted seismic reflection/refraction profiles from JAMSTEC.

Felt-, lab- og analyse- arbeid/Field-work, lab-analysis
Numerical modelling of seafloor deformatio above subduction zones.

Proposed course plan during the master degree

GEOV255 - Seismotektonikk
GEOV276 - Teoretisk seismologi
GEOV359 - Prosessering av jordskjelvsdata
GEOV355 - Anvendt seismologi
GEOV219 - Computational methods in solid Earth physics