A study on the characteristic relaxation time of 2011 Tohoku-Oki earthquake

based on GRACE data

Author: Yuting Ji �Wenke Sun �He Tang Reporter: Yuting Ji University of Chinese Academy of Sciences

August, 2019 Lugu Lake, China

Outline

Background and Issues

Situation and Development Issues

Conclusion and References

01

04

03

02

Research Processes and Results

Part 01 Background and Issues

01 Background and Issues

From USGS Official Data, 2011 Tohoku-Oki earthquake is a giant earthquake with a magnitude of

9.0

The epicenter is (142.4°E�38.3°N).

>

The depth is 29km under surface.>

It occurred at the Pacific Plate subducts

beneath northeast Japan.>

The fault type is reverse fault> (Wang, Hu et al. 2012)

01 Background and Issues

GRACE satellites

GRACE(Gravity Recovery and Climate Experiment): can provide continuous model of the earth gravity field.

Glacier and ocean water changes

Ice sheet mass changes

Groundwater movements

.

.

.

Solid earth structure changes

Through various experimental studies, GRACE can detect the large-scale mass migration

caused by the coseismic rupture of large earthquakes in the global subduction zone and

the viscoelastic relaxation of the mantle after the earthquakes.

Part 02 Situation and Development Issues

02 Situation and Development Issues

(Sun, Wang et al. 2014)

In Sun and wang’s study in 2014, they use the land and seafloor GPS sites’ movement to monitor the coseismic and the postseismic deformation by setting up the two-dimensional rheology model.

GPS

02 Situation and Development Issues

A two exponential decay functions are applied to model the postseismic change

GRACE

(Tanaka and Heki 2014)

Part 03 Research Processes and Results

03 Research Processes and Results

Data

Filter

Gaussian filter 300 km

In order to remove the influence of high frequency noise.

P4M6 De-correlation filter

Remove the north and south strip noise in GRACE signal.

We use 156 months of GRACE RL05 Level-2 data released

by CSR from 2002.09 to 2017.03.

The data used do not include the month in which the

earthquake occurred, and the missing data.

03 Research Processes and Results

Co-seismic gravity changes: Negative in north-west , positive in south-east

Co-seismic gravity values : ~-6 micro Gal --- ~3 micro Gal

03 Research Processes and Results

The exponential decay function we used to fit the data of single time series.

1 2sin( ) sin(2 ) ( ) 1 exp( )tg A Bt C t D t H t E Fw q w qt

ì D üé ùD = + + + + + + D + - -í ýê úë ûî þ

A B

Black curve: the original monthly gravity change

Blue curve: including periodic signals, coseismic jumps and postseismic exponential decay

Red curve: including co-seismic jumps and postseismic exponential decay

03 Research Processes and Results

�Zhou et al., 2018�

Characteristic relaxation time distribution of 2011 Tohoku-Oki earthquake

Part 04 Conclusion and References

04 Conclusion and References

Characteristic Relaxation time of the post-seismic is a quite long time scale. And as the

dominance of the postseismic deformation, it normally needs several years to recover.

Characteristic Relaxation time are related to the tectonic, the thickness of the oceanic

crust is thinner, and due to it constantly moving, the area of it responds more quickly to

the mantle viscoelastic relaxation. However, the continental crust is thicker, and with the

subduction of the oceanic crust, the viscoelastic relaxation occurs in the deeper region

after the earthquake, so the response to the viscoelastic behavior is slow.

In our study, we use the 156 monthly average time-varying gravity field data of GRACE

RL05 Level-2 and applying a 300km Gaussian filter and a P4M6 de-correlation filter, the

results of coseismic and long-term postseismic gravity change of 2011 Tohoku-Oki

earthquake are obtained by using the method of mean subtraction and least squares.

04 Discussion and References

References:[1] Tanaka, Y. & K. Heki (2014) Long- and short-term postseismic gravity changes of megathrust earthquakes from satellite gravimetry. Geophysical Research Letters, 41, 5451-5456.[2] Zhou, X., G. Cambiotti, W. Sun & R. Sabadini (2018) Co-seismic slip distribution of the 2011 Tohoku(M_W 9.0)earthquake inverted from GPS and space-borne gravimetric data. Earth and Planetary Physics, 2, 120-138.[3] Yamagiwa, S., S. i. Miyazaki, K. Hirahara & Y. Fukahata (2015) Afterslip and viscoelastic relaxation following the 2011 Tohoku-oki earthquake (Mw9.0) inferred from inland GPS and seafloor GPS/Acoustic data. Geophysical Research Letters,42, 66-73.[4] Sun, T., K. Wang, T. Iinuma, R. Hino, J. He, H. Fujimoto, M. Kido, Y. Osada, S. Miura, Y. Ohta & Y. Hu (2014) Prevalence of viscoelastic relaxation after the 2011 Tohoku-oki earthquake. Nature, 514, 84.[5] Matsuo, K. & K. Heki (2011) Coseismic gravity changes of the 2011 Tohoku-Oki earthquake from satellite gravimetry. Geophysical Research Letters, 38.[6] Diao, F., X. Xiong, R. Wang, Y. Zheng, T. R. Walter, H. Weng & J. Li (2014) Overlapping post-seismic deformation processes: afterslip and viscoelastic relaxation following the 2011 Mw 9.0 Tohoku (Japan) earthquake. Geophysical Journal International, 196, 218-229.