Spatiotemporal functional modeling of postseismic deformations after the 2011 Tohoku-Oki earthquake

Satoshi Fujiwara,Mikio Tobita,Shinzaburo Ozawa

doi:10.1186/s40623-021-01568-0

Satoshi Fujiwara, Mikio Tobita + Show 1 more

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https://doi.org/10.1186/s40623-021-01568-0

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Abstract

Postseismic deformations continue to occur for a long period after major earthquakes. Temporal changes in postseismic deformations can be approximated using simple functions. Since the 2011 Tohoku-Oki earthquake, operating global navigation satellite system stations have been continuously accumulating a remarkable amount of relevant data. To verify the functional model, we performed statistical data processing on postseismic deformations due to this earthquake and obtained their spatiotemporal distribution. Moreover, we approximated the postseismic deformations over a relatively wide area with a standard deviation of residuals of 1 cm for approximately 10 years using a combined functional model of two logarithmic and one exponential functions; however, the residuals from the functional model exhibited a marked deviation since 2015. Although the pattern of postseismic deformations remained unaltered after the earthquake, a change in the linear deformation occurred from 2015 to date. We reduced the overall standard deviation of the residuals of > 200 stations distributed over > 1000 km to < 0.4 cm in the horizontal component by enhancing the functional model to incorporate this linear deformation. Notably, time constants of the functions were similarly applicable for all stations and components. Furthermore, the spatial distribution of the coefficients of each time constant were nonrandom, and the distribution was spatially smooth, with minute changes in the short wavelengths in space. Thus, it is possible to obtain a gridded model in terms of a spatial function. The spatial distributions of short- and long-period components of the functional model and afterslip and viscoelastic relaxation calculated using the physical model were similar to each other, respectively. Each time function revealed a connotation regarding the physical processes, which provided an understanding of the physical phenomena involved in seismogenesis. The functional model can be used to practical applications, such as discerning small variations and modeling for precise positioning.Graphical

Highlights

IntroductionOn March 11, 2011, an earthquake of magnitude (M) 9 hit the Pacific coast near Tohoku, Japan and caused coseismic crustal displacement of > 5 m in the horizontal direction and > 1 m in the vertical direction
Concluding remarks The functional model for the postseismic deformation of large earthquakes by Tobita (2016) with statistical processing using a model with two logarithmic functions and one exponential function allows us to draw the following conclusions: (1) The functional model can predict the postseismic deformation of the 2011 Tohoku-Oki earthquake with good accuracy even after 10 years over a wide area exceeding 1000 km
(2) The same time constants of the time function are applicable for all observation stations and components; when these time constants change, the distribution of the spatial function for each time function varies at a certain rate for all observation stations, absorbing the change in the total functional model

Summary

Introduction

IntroductionOn March 11, 2011, an earthquake of magnitude (M) 9 hit the Pacific coast near Tohoku, Japan (hereinafter, the 2011 Tohoku-Oki earthquake) and caused coseismic crustal displacement of > 5 m in the horizontal direction and > 1 m in the vertical direction. Large postseismic crustal displacements of > 1 m continued to occur, depending on the location (Ozawa et al 2011; 2012). As understanding the spatiotemporal distribution of postseismic deformations enables accurate estimation of seismogenic processes, such functional models are beneficial for forecasting seismic activity and understanding the physical mechanism of large earthquakes. They are useful for discerning small crustal deformations caused by other sources by removing large postseismic deformation. The functional model has been utilized by Ozawa et al (2016), Sakaue et al (2019), and others to discern crustal deformations other than postseismic deformations of large earthquakes

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