Key Points:• A long-term data set spatial-temporal infrasound propagation is presented • Numerical modeling with atmosphere and topography explains the observation • The propagation effects are nonnegligible and can be evaluated by our model Abstract The effects of topography and atmospheric structures on infrasonic wave propagation from a volcanic source were investigated using observations and numerical modeling. This paper presents the first long-term observational data set showing spatiotemporal variations in patterns of infrasound propagation at distances of up to 60 km from a persistently active infrasound source (Sakurajima Volcano, Japan). The data show that the amplitudes of infrasonic waves received at distant stations relative to those received at a reference station close to the source can vary up to an order of magnitude over short time intervals and short distances and that they do not follow the theoretical geometric decay expected for homogeneous media. Moreover, waveforms also change significantly in both time and space. Numerical simulations were performed using a two-dimensional finite difference time domain (2-D FDTD) method. Effects of atmospheric structure and topography are included in a vertical section parallel to the wave propagation direction. The simulation successfully reproduced the variations of amplitudes and waveforms. Results are interpreted in terms of wave refraction due to sound and wind speed gradients and wave diffraction at topographic barriers. Our numerical results indicate that both atmospheric and topographic propagation effects are nonnegligible. To evaluate the propagation effects and determine source processes in spatially and temporally varying infrasound data, atmospheric data with a time resolution higher than is currently available are required. If the data are available, the present results suggest that the propagation effects could be evaluated using 2-D FDTD modeling at realistic calculation times.

Atmospheric pressure changes caused by the 2011 Off the Pacific Coast of Tohoku, Japan earthquake (Mw = 9.0) are investigated. Sensitive microbarographs in and around Japan recorded unequivocal signals associated with the tsunami. We identify them as atmospheric boundary waves excited by the uplift and subsidence of the ocean surface, on the basis of the waveform characteristics as well as similarity with the data from ocean‐bottom pressure gauges. Potential usefulness of an observation network of atmospheric pressure is discussed regarding the improvement of the tsunami warning system.

The Indochina peninsula has been hypothesized to be in the Sunda block, a rigid block in SE Asia. However, its northern boundary is not obvious. To elucidate the boundary and the deformation on the peninsula, six permanent GPS sites were established in Thailand, and observations have been conducted since March 1998. Estimated velocities suggest that most of the Indochina peninsula is rigid and can be considered in the Sunda block. However, close examination suggest small but significant strain in the order of 10−8 exists in Thailand. Statistical test suggests that there is no significant differential motion between the Sunda block and the South China block. On the other hand, acute clockwise rotation of east Himalayan syntax indicates left lateral shear in the north of Thailand, which may be partially accommodated by left lateral motion along Mae Chan fault.

An intermediate-strength earthquake of magnitude M j 6.8 occurred on July 16, 2007, centered beneath the Japan Sea a few kilometers offshore of Niigata Prefecture in central Japan. We constructed a dense GPS network to investigate postseismic deformation after this event, choosing our GPS sites carefully so as to complement the nationwide GPS GEONET array. Coseismic displacements caused by the mainshock detected at some GEONET sites were used to estimate coseismic fault parameters. The results indicate that the geodetic data can be explained by a combination of two rectangular faults dipping northwest and southeast. Minor but definite postseismic deformation was detected largely in the southern part of the dense network. The time series of site coordinates can be characterized by a logarithmic decay function, and the estimated time constant seems to be almost similar in range to that of the 2004 Mid-Niigata Prefecture Earthquake. We also found a possible site instability at 960566 (Izumo-zaki, GEONET) caused by a small, local landslide associated with the mainshock and therefore concluded that the data obtained at this site should not be used for coseismic or postseismic analysis.