Spatial distribution of seismicity has hitherto been visualized on two-dimensional maps and vertical cross-sections along certain lines so far. Owing to the advances in technology, we have developed a mobile application for iPhone and iPad devices, which can display the seismicity of Japan in three-dimensional (3D) view. Each hypocenter is plotted as a 3D spherical object whose color and size represented its depth and magnitude, respectively. The geometry of the Philippine Sea Plate and the Pacific Plate can be plotted as 3D polygons with the hypocenters, simultaneously. In addition to those plate boundaries, the topography of Japan and the ocean bathymetry around it are also plotted as a 3D polygon. The 3D image of the hypocenters and plate geometries helps users to perceive intuitively the spatial distribution of earthquakes such as that many earthquakes occur along the subducting plates. Moreover, the spatiotemporal distribution of seismicity can be seen by the time-lapse animation of hypocenters. The hypocenter catalog can be downloaded through the Internet by using the account of NIED MOWLAS. More than one month’s earthquakes (18,000 events) can be displayed smoothly.

The 2018 northern Osaka Prefecture earthquake (M_j 6.1) was caused by ruptures of blind strike-slip and reverse faults. The earthquake was moderate in size but caused severe damages to the northeastern part of the densely populated Osaka metropolitan area. The epicentral area is located at a junction of east-trending strike-slip faults and north-trending reverse faults. In order to better understand the geologic setting of the earthquake, we conducted an integrated analysis of published seismic reflection profiles and gravity basement structure map together with geomorphic and geologic data. We interpreted that the Arima-Takatsuki Tectonic Line fault zone extends about 9 km further to the east of the geomorphologically mapped surface trace. We also found that the Hirakata flexure extends northeast beneath the Yodo River as a southeast-dipping reverse fault. The area bounded by the Arima-Takatsuki Tectonic Line fault zone and northeast extension of the Hirakata flexure is a northeast-trending graben which we call here as the Yodogawa graben. The 2018 earthquake occurred beneath the graben but the ruptured faults do not offset gravity basement. The identification of the previously unknown active faults warrants further geological and geophysical studies of the faults in this highly urbanized area of the Osaka Plain.

In leap July of the 5th year of Bunroku (in the old Japanese calendar; mostly September, 1596 in the Gregorian calendar) Bungo province (present-day Oita Prefecture) in Kyushu, southwest Japan, suffered from severe earthquake and tsunami disasters. Concerning the occurrence date of the causative earthquake, the prevailing idea is currently that a large earthquake took place on leap July 9 (September 1, 1596) in Iyo province (present-day Ehime Prefecture) in Shikoku, on the eastward opposite shore of Bungo, and another large earthquake occurred on leap July 12 in Bungo. Against this idea, I claim that a single event which can be called “the Iyo-Bungo earthquake” occurred around seven p.m. on leap July 9 in the Iyo-Bungo region based on reliable contemporary historical records. There are 69 documents on this (these) earthquake(s) printed in the existing collections of historical earthquake materials, but their values as historical records vary considerably. Since the essential principle of historiographical seismology is to utilize only reliable first-grade documents, I performed historical source criticism to select 16 contemporary materials. I referred to their original or best texts, not using texts printed in the collections. According to a record in Bungo violent ground motion collapsed shrine buildings around seven to nine p.m. on leap July 9 and a large tsunami hit Fuchu (Oita) in the twilight. In Kyoto, an autograph diary of a court noble, which is used for the first time in historical seismology, describes considerable earthquake motion around seven p.m. on leap July 9. In Hiroshima Prefecture, at Hatsuka-ichi and Itsukushima strong ground motions were felt at night on leap July 9 without damages, and at Mihara strong tremors continued from leap July 9 till 12. In Iyo, a contemporary record says a severe ground motion occurred on leap July 9 and the whole Iyo province had trouble, suggesting earthquake damages in a wide area. In Satsuma and Osumi provinces (present-day Kagoshima Prefecture), a record tells a strong earthquake on leap July 9. As a fundamental methodology of historiographical seismology, these tremors and tsunami in Bungo, Iyo, Kyoto, Hiroshima and Kagoshima on leap July 9 are considered to have been produced by an identical earthquake unless there is any counter-evidence. Leap July 12, the other proposed date of the Bungo earthquake, comes from historical materials written after 1698, which probably mistook the great Kyoto earthquake in the midnight of leap July 12 for the Bungo event. Seismic intensities are estimated to be 6 in Bungo, stronger than or equal to 5 in Iyo, 4 in Hiroshima Prefecture, 3 in Kyoto, and about 4 in Kagoshima on the JMA scale (1949-1996 version). The most simple and reasonable interpretation is that a large earthquake with the source region from around Beppu Bay off Bungo to the offshore area of western Iyo, a part of the Median Tectonic Line fault zone, took place around seven p.m. on leap July 9, whose inferred magnitude being about 7.5 (corresponding to M_JMA), and the tsunami on the Bungo coast followed.