Figure 4

Gravity changes and northern gravity gradient changes with the mean of 2 years' synthetic data. The changes are between the mean of 2 years before and after the earthquake, computed from the synthetic monthly GRACE observations (with seasonal and trend terms removed by time series fitting), with 300 km Gaussian smoothing only (without destriping). (a) Near-field gravity changes. (b) Global gravity changes with cell size of 1° × 1°, in which the black rectangle denotes the region in (a). (c) Near-field northern gravity gradient changes. (d) Global northern gravity gradient changes. (e) Time series of the synthetic monthly GRACE gravity values at points A (38.5°N, 139.0°E) and B (38.0°N, 146.5°E) marked as white triangles in (a), from January 2007 to February 2011. (f) Time series of the synthetic monthly GRACE gravity gradient values at points C (41.5°N, 138.5°E), D (36.0°N, 139.5°E), and E (34.3°N, 146.0°E) marked as white triangles in (c). The time series are fitted by two linear terms before and after the earthquake, the annual and semiannual periodic terms, and a coseismic step term. The linear trends before and after the earthquake as well as the coseismic jumps are shown with the solid lines. The vertical green line represents the occurrence month of the synthetic earthquake (i.e., March 2009). The magenta rectangles in (b) and (d) denote the region of the near field in (a) and (c).