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A short-baseline weather radar network consisting of Ku-band broadband radars (BBR) for meteorological application is under development. The BBR is a short-range and high-resolution Doppler radar for meteorological application, whose range and temporal resolution are several meters and 1 min per volume scan, respectively and coverage is from 50 m to 15 or 20 km. A radar network consisting of BBRs is useful for rapidly and accurately detecting and analyzing small-scale weather phenomena such as localized scattered thunderstorms, tornadoes, and downbursts in locations with a complex topography such as urban or mountainous area. The BBR network project plans to deploy three BBRs in the north Osaka, Japan, area and to observe and analyzing small-scale weather phenomena in detail. At present, two functioning BBRs have been deployed in the Osaka area. This paper presents a description of the BBR network project and its preliminary assessment. Observations of the two-BBR test bed derive expected properties of the three-BBR network, which efficiently covers troposphere in the overlapped area with a minimum observable altitude of tens of meters and a sensitivity of 10.2 dBZ (spatial average at a 5000-km altitude). Integrated reflectivity and preliminary algorithm for multiradar products in the two-BBR test bed, presenting a promising fine structure of precipitation cells, is also shown. [ABSTRACT FROM AUTHOR]

We reconstructed the spatiotemporal evolution of seismicity associated with the 2018 Mw 5.6 northern Osaka earthquake, Japan, to discuss the source fault model of the mainshock rupture, the possible link between this rupture and known active faults, and subsequent crustal deformation. We first relocated the hypocenters listed in the earthquake catalog determined by the Japan Meteorological Agency using a double-difference relocation algorithm. We then searched for the earthquake waveforms that closely resembled those of the relocated hypocenters by applying a matched filtering technique to the continuous waveform data. The relocated hypocenters revealed two distinct planar alignments with different fault geometries. A combination of the relocated hypocenters and focal mechanisms suggests that the mainshock rupture initiated on a NNW-SSE-striking thrust fault, dipping ~ 45° to the east, with the rupture propagating to an adjacent sub-vertical ENE-WSW-striking strike-slip fault ~ 0.3 s after the initial mainshock rupture, resulting in the simultaneous propagation of dynamic rupture along the two faults. The strike-slip fault is oblique to the strike of the Arima-Takatsuki Fault, indicating that blind strike-slip faulting occurred. While the east-dipping thrust fault is located deeper than the modeled extent of the Uemachi Fault, a simple extrapolation of the near-surface geometry of the Uemachi fault partially overlaps the mainshock rupture area. Although it is unclear as to whether a blind thrust fault or a deep portion of the Uemachi Fault ruptured during this mainshock-aftershock sequence, a mainshock rupture would have transferred a static stress change of > 0.1 MPa to a portion of the east-dipping thrust fault system. Intensive aftershocks have persisted along the northern and southern edges of the source area, including moderate-magnitude events, whereas the seismicity in the central part of the source area has shown a rapid decay over time. Delayed triggered aftershocks were clearly identified along the northern extension of the rupture area. Because the background seismicity is predominant in this northern area, we interpret that aseismic deformation, such as cataclastic flow lubricated by crustal fluids, triggered this off-fault seismicity. [ABSTRACT FROM AUTHOR]