We observed a 17@ ] 17@ region of the o Oph molecular cloud, using the ACIS-I array on board the Chandra X-Ray Observatory. A 100 ks exposure observation revealed D100 X-ray sources above the detection limit of D1028 ergs s~1. About two-thirds of the X-ray sources are identiÐed with an optical and/or IR counterpart, including signiÐcant numbers of class I, II, and III sources and a few brown dwarfs. The X-ray detection rate of class I sources is a surprisingly high 70%. Many X-ray Ñares, possibly because of the magnetic activity, are found from all of the classes. We make systematic spectral studies of the quiescent and Ñare X-rays for all the X-ray sources. The X-ray temperatures and absorptions of class I sources are generally larger than those of class II and III sources. In addition, X-ray Ñares from class I sources show slightly higher duty ratio, temperature, and luminosity than those of more evolved classes. We further give brief results on brown dwarfs, sources in a younger phase than class I, unclassiÐed, and unidentiÐed sources. Details for several selected young stellar objects, including the Ðrst detection of a neutral iron line (6.4 keV) from a class I source (YLW 16A), are separately addressed.

Recently observed unusual seismic events: deep low frequency earthquakes and tremor, very low frequency earthquakes, and slow slip events form a family of slow earthquakes that are governed by a scaling law different from ordinary earthquakes. Guided by this scaling law, we have observed previously unknown events, with source duration of 20–200 s and moment magnitude of 3–4, under the Kii Peninsula in western Japan. These events radiate seismic energy in the 2–8 Hz band in direct proportion to their seismic moment‐rate, though the constant of proportionality is 4–5 orders of magnitude smaller than for ordinary earthquakes. Slow earthquakes in this region may be comprised of numerous shear slip events, which in aggregate are manifest seismically as tremor or isolated longer events up to 200 s and geodetically as slow slip events.

No abstract

The 2016 Kumamoto earthquake sequence started with a M J (Japan Meteorological Agency magnitude) 6.5 event on April 14, and culminated in a M J 7.3 event on April 16. Associated with the sequence, approximately 34-km-long surface ruptures appeared along the eastern part of the Futagawa fault zone and the northernmost part of the Hinagu fault zone. We carried out an urgent field investigation soon after the earthquake to map the extent and displacement of surface ruptures with the following results. (1) The rupture zone generally consisted of a series of left-stepping en echelon arrays of discontinuous fault traces of various lengths. (2) Slip exceeding 100 cm occurred on previously unrecognized fault traces in the alluvial lowland of the Kiyama plain and on the western rim of the Aso volcano caldera. (3) Large slip with maximum dextral slip of 220 cm was measured throughout the central section of the rupture zone along the Futagawa segment, and the slip gradually decreased bilaterally on the adjoining northeastern and southwestern sections. (4) The surface rupture mostly occurred along fault traces mapped in previous active fault investigations. (5) Most of the surface ruptures were produced by the mainshock, and significant postseismic slip occurred after the mainshock.