Summary
This report presents the results of the project “Research on rapid estimation of the parameters for large
earthquakes along trenches”, which was conducted by the Seismology and Tsunami Research Department, MRI,
over six years from FY 2010 to FY 2015. The report consists of four chapters.
Chapter 1: Estimation of earthquake magnitude and related parameters
Chapter 2: Estimation of fault rupture length and slip distribution
Chapter 3: Estimation of aftershock distribution
Chapter 4: Estimation of distribution of strong ground motion
Chapter 1 reports on methods of rapid estimation of earthquake magnitude and source parameters that weredeveloped to overcome difficulties encountered during determination of the magnitude of the 2011 off thePacific coast of Tohoku Earthquake (2011 Tohoku earthquake hereafter). Section 1.1 describes various
methods for the rapid determination of magnitude of great earthquakes. Section 1.2 describes a method ofmagnitude estimation based on peak ground displacement for various cut-off periods. Section 1.3 describes thecharacteristics of rupture propagation inferred from the duration of strong motion. Section 1.4 describes amethod for categorizing focal mechanisms.
Chapter 2 reports on methods for rapid estimation of the length of rupture of the earthquake fault and the slip
distribution. Section 2.1 describes a method for estimation of the length of rupture of the earthquake fault fromthe distribution of seismic intensity. Section 2.2 describes a method to estimate the area of large coseismic slipby using an array technique for long-period seismic waves. Section 2.3 describes the source process analysis
for the 2011 Tohoku earthquake. Section 2.4 describes the source process analyses for major aftershocks of the2011 Tohoku earthquake. Sections 2.5 and 2.6 describe real-time methods for estimation of tsunami source
parameters using both of onshore GNSS data and offshore tsunami data.
Chapter 3 reports on methods of hypocenter determination, related studies of aftershocks, and improvementsin the precision of hypocenter determinations. Section 3.1 describes an automated method of hypocenter
determination that uses Bayesian analysis. Section 3.2 describes an automated method for estimation ofaftershock distributions by using envelope data. Section 3.3 describes seismicity recorded by pop-up OBSs inthe outer rise area of the Nankai trough. Section 3.4 describes long-term pop-up OBSs that were developed toimprove seismic observation data in offshore areas. Section 3.5 describes a crustal structure model of theJapanese islands estimated to improve the precision of hypocenter determinations. Section 3.6 describes amethod for fast determination of hypocenters by using 3D traveltime tables. Section 3.7 describes seismicity
activated after the 2011 Tohoku earthquake in various areas of Japan.
Chapter 4 reports on methods for estimation of the distribution of strong ground motion. Section 4.1
describes the relationship between subsurface structure and ground motion of various periods. Section 4.2
describes the strong ground motion of the 2011 Tohoku earthquake. Section 4.3 describes a method for
estimation of seismic wave propagation by using a data assimilation technique.
Some of the methods described here have been used to improve tsunami warnings since March 2013.