Masumi Yamada

We use broadband seismic recordings to trace the dynamic process of the deep‐seated Akatani landslide that occurred on the Kii Peninsula, Japan, which is one of the best recorded large slope failures. Combining analyses of the seismic records with precise topographic surveys done before and after the event, we can resolve a detailed time history of the mass movement. During 50 s of the large landslide, we observe a smooth initiation, acceleration with changes in basal friction, and reversal of t

Large deep‐seated landslides occurred in Nara, Wakayama, and Mie prefectures of western Japan when Typhoon Talas passed through the region on September 3–4, 2011. Signals of large landslides have been recorded by seismic networks around the world, and overall force estimates have been previously determined for large landslides using long‐period waves. This study focuses on the high‐frequency waveforms and presents signals of 18 landslides caused by Typhoon Talas (2011). The location of the lands

The 2016 Kumamoto earthquakes caused serious building damage in Mashiki town. Because two large earthquakes occurred within an interval of 28 hours, it is difficult to separate the damage caused by each of these earthquakes. We analyzed aerial photos of the center of Mashiki town taken before and after the second event, which allow us to separate the damage caused by the two earthquakes. Our analysis shows that building damage was concentrated especially on the river terrace of the Akitsu river,

Abstract A precursory sequence of repeating earthquakes was recorded before the Rausu landslide in Hokkaido, Japan, on 24 April 2015. There were two seismic sequences with each consisting of very similar waveforms and leading up to significant landslide movements. The nearly identical waveform shapes indicate similar source locations and mechanisms, so repeated events originated on a particular small area. This sequence is interpreted as stick‐slip movement on a small patch leading up to the lar

Abstract The 2022 volcanic eruption in Tonga caused an unusually large tsunami around the Pacific. It travels with a faster apparent velocity and has larger amplitudes at long distances than what would be expected from a conventional tsunami from the volcanic source. This tsunami was generated by the moving atmospheric Lamb wave and traveled at the speed of the Lamb wave (0.31 km/s). Japanese data showed the amplitude of this first tsunami becomes small when approaching the coast, due to the wea

To estimate the fault dimension of an earthquake in real time, we present a methodology to classify seismic records into near-source or far-source records. Characteristics of ground motion, such as peak ground acceleration, have a strong correlation with the distance from a fault rupture for large earthquakes. This study analyzes peak ground motions and finds the function that best classifies near-source and far-source records based on these parameters. We perform (1) Fisher’s linear discriminan

We apply a deconvolution method to a strong motion data set recorded at the surface and in boreholes in northeast Honshu, Japan. We try to characterize the nonlinear effects of the subsurface soil during strong shaking and show the change of the subsurface velocity structure during the shaking. The deconvolved waveforms reflect the subsurface velocity structure, and their horizontal and vertical components correspond to S and P wave, respectively, traveling from the borehole to the ground surfac

The 2008 Iwate-Miyagi Nairiku earthquake (M_w 6.9, M_(jma) 7.2) produced strong shaking throughout northern Honshu, Japan, with severe damage to buildings and extensive landslides. The shallow event occurred in southwestern Iwate Prefecture (39.03°N, 140.88°E, depth 8 km) on 13 June 2008 at 23:43:45 GMT (Japan Meteorological Agency 2008). This earthquake produced relatively high-frequency ground motions, which resulted in large values of peak ground acceleration (PGA). The surface accelerometer

We performed numerical simulations of the 2011 deep-seated Akatani landslide in central Japan to understand the dynamic evolution of friction of the landslide. By comparing the forces obtained from numerical simulation to those resolved from seismic waveform inversion, the coefficient of the friction during sliding was investigated in the range of 0.1–0.4. The simulation assuming standard Coulomb friction shows that the forces obtained by the seismic waveform inversion are well explained using a

This paper analyzes strong motion records of 24 large earthquakes to investigate the relationship between τ c (the period parameter of the first motion) and moment magnitude. The records of some of the large‐magnitude events very close to the source include large near‐field terms. Therefore, if we include the data with large near‐field terms, we may overestimate the final size of the magnitude. We identified records with large near‐field terms and did not include these data in processing the rec

This study collects recorded ground motions from the near-source region of large earthquakes and considers to what extent this historic record can inform expectations of future ground motions at similar sites. The distribution of observed peak ground acceleration (PGA) is well approximated by the lognormal distribution, and we expect the observed distribution to remain unchanged with the addition of data from future earthquakes. However, the distribution of peak ground displacements (PGD) will l

We present a new strategy to estimate the geometry of a rupture on a finite fault in real time for earthquake early warning. We extend the work of Cua and Heaton who developed the virtual seismologist (VS) method (Cua, 2005), which is a Bayesian approach to seismic early warning using envelope attenuation relationships. This article extends the VS method to large earthquakes where fault finiteness is important. We propose a new model to simulate high-frequency motions from earthquakes with large

ABSTRACT In this article, we created a well-resolved aftershock catalog for the 2015 Gorkha earthquake in Nepal by processing 11 months of continuous data using an automatic onset and hypocenter determination procedure. Aftershocks were detected by the NAMASTE temporary seismic network that is densely distributed covering the rupture area and became fully operational about 50 days after the mainshock. The catalog was refined using a joint hypocenter determination technique and an optimal 1D velo

ABSTRACT The 2018 Mw 6.4 Hualien earthquake generated a large peak-to-peak velocity of over 2 m/s, with a period of 3 s at the south end of the Milun fault, which resulted in the collapse of five buildings. To investigate the shallow subsurface soil structure and evaluate possible effects on the ground motion and building damage, we performed microtremor measurements in the Hualien basin. Based on the velocity structure jointly inverted from both Rayleigh-wave dispersion curves and microtremor h