地震前に見らるゝ魚類の異常生態に就ての二三の観察

As we are so often visited by terrible earthquakes, the unusual phenomena of the natural world accompanying them have long been observed by many scientists as well as laymen. Accordingly, papers dealing with the abnormal behaviour of fishes prior to an earthquake are exceedingly numerous all of which have been systematically embodied in the report of Mr. K. Musya. Prof. T. Terada. has recently made a statistical investigation of the effects of the Idu earthquakes eu the horse-mackerel and bluefin tuna fisheries, Prof. S. Hatai has studied biologically the responses of the catfish to earthquakes. All these studies equally prove the existence of a mysterious and instinctive reaction of the fish to earthquakes.筆者は彼の三陸大地震發生の當時,地震の前夕及び3日後,三崎近海の表層で,眞鰮,Sardina melanosticta,の成魚を採集した.胃内容物を査定した所前者は表Iに示したる如く専ら多量の底着性硅藻類を,後者は表IIに示したる如く適量の浮遊生物を攝取して居るのを發見した.然るに岸上先生の報告にも明かである如く,眞鰮は常時,少くも此季節では,浮遊生物を適量攝取するのが普通である.してみると前者の揚合,即ち地震發生に先立つて,海の表層に多量の底着性硅藻類が出現して居たと考へなくてはならぬ.昭和8年3月3日三陸地方津浪に関する論文及報告　第1編　論

Normal faulting of the Daiichi-Kashima Seamount in the Japan Trench revealed by the Kaiko I cruise, Leg 3

International audienceA detailed topographic and geophysical survey of the Daiichi-Kashima Seamount area in the southern Japan Trench, northwestern Pacific margin, clearly defines a high-angle normal fault which splits the seamount into two halves. A fan-shaped zone was investigated along 2-4 km spaced, 100 km long subparallel tracks using narrow multi-beam (Seabeam) echo-sounder with simultaneous measurements of gravity, magnetic total field and single-channel seismic reflection records. Vertical displacement of the inboard half was clearly mapped and its normal fault origin was supported. The northern and southern extensions of the normal fault beyond the flank of the seamount were delineated. Materials on the landward trench slope are displaced upward and to sideways away from the colliding seamount. Canyons observed in the upper landward slope terminate at the mid-slope terrace which has been uplifted since start of subduction of the seamount. Most of the landward slope except for the landward walls aside the seamount comprises only a landslide topography in a manner similar to the northern Japan Trench wall. This survey was conducted on R/V "Jean Cbarcot" as a part of the Kaiko I cruise, Leg 3, in July-August 1984 under the auspices of the French-Japanese scientific cooperative program

The Japan Trench and its juncture with the Kuril Trench: cruise results of the Kaiko project, Leg 3

International audienceThis paper presents the results of a detailed survey combining Seabeam mapping, gravity and geomagnetic measurements as well as single-channel seismic reflection observations in the Japan Trench and the juncture with the Kuril Trench during the French-Japanese Kaiko project (northern sector of the Leg 3) on the R/V "Jean Charcot". The main data acquired during the cruise, such as the Seabeam maps, magnetic anomalies pattern, and preliminary interpretations are discussed. These new data cover an area of 18,000 km 2 and provide for the first time a detailed three-dimensional image of the Japan Trench. Combined with the previous results, the data indicate new structural interpretations. A comparative study of Seabeam morphology, single-channel and reprocessed multichannel records lead to the conclusion that along the northern Japan Trench there is little evidence of accretion but, instead, a tectonic erosion of the overriding plate. The tectonic pattern on the oceanic side of the trench is controlled by the creation of new normal faults parallel to the Japan Trench axis, which is a direct consequence of the downward flexure of the Pacific plate. In addition to these new faults, ancient normal faults trending parallel to the N65 ° oceanic magnetic anomalies and oblique to the Japan trench axis are reactivated, so that two directions of normal faulting are observed seaward of the Japan Trench. Only one direction of faulting is observed seaward of the Kuril Trench because of the parallelism between the trench axis and the magnetic anomalies. The convergent front of the Kuril Trench is off~t left-laterally by 20 km relative to those of the Japan Trench. This transform fault and the lower slope of the southernmost Kuril Trench are represented by very steep scarps more than 2 km high. Slightly south of the juncture, the Erimo Seamount riding on the Pacific plate, is now entering the subduction zone. It has been preceded by at least another seamount as revealed by magnetic anomalies across the landward slope of the trench. Deeper future studies will be necessary to discriminate between the two following hypothesis about the origin of the curvature between both trenches: Is it due to the collision of an already subducted chain of seamounts? or does it correspond to one of the failure lines of the America/Eurasia plate boundary