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Volume 43, Issue 11
Displaying 1-6 of 6 articles from this issue
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N. Fukushima1991 Volume 43 Issue 11 Pages 883-884
Published: 1991
Released on J-STAGE: August 11, 2011
JOURNAL FREE ACCESSDownload PDF (491K) -
G. G. BOWMAN1991 Volume 43 Issue 11 Pages 885-897
Published: 1991
Released on J-STAGE: September 14, 2010
JOURNAL FREE ACCESSThe main aim of this paper is to discuss and illustrate why the occurrence of diffuse mid-latitude spread-F ionograms suggests scattering from small-scale ionospheric structures as the primary cause of the spread, contrary to present ideas involving duplicate traces as the basic trace structures on sonograms. A number of factors which modify duplicate traces and tend to produce diffuseness are described. Sometimes these factors, which mainly involve interference effects due to overlapping traces, are so dominant that the diffuseness obscures any trace of the duplicate traces. In addition an important factor is the periodic replacement (sometimes recorded) of the quasi-horizontal-trace (QHT) segments of the duplicate traces (reported earlier for daytime events). These effects which are detected on fixed-frequency ionograms suggest that dynamic changes are occurring to ionospheric structures over and above those normally expected during the passage of a travelling ionospheric disturbance.View full abstractDownload PDF (1558K) -
G. G. BOWMAN1991 Volume 43 Issue 11 Pages 899-920
Published: 1991
Released on J-STAGE: September 14, 2010
JOURNAL FREE ACCESSSeveral diverging duplicate traces and one converging duplicate trace for mild mid-latitude spread-F events (on one particular night) have been used to investigate medium-scale travelling ionospheric disturbances (TIDs) during night hours. Swept-frequency and fixed-frequency sonograms (which have phase information added) show spread-F characteristics similar to those recorded for more intense spread-F events. These include modulated height rises in the isoionic contours and electron-density depletions. The phase-path information on the fixed-frequency recordings allowed the detection of the TID wavetrains responsible for the modulation. Usually for these mild events one tilt in the isoionic contours produced by one cycle of a wavetrain is sufficiently large to allow significant off-vertical reflections which in turn are responsible for a diverging trace. Speeds of travel have been determined by considering both the rate of change of group-range for the duplicate traces as well as the rate of change of phase-path indicated on each fixed-frequency recording. The speeds of travel of these nighttime TIDs are compared with the speeds of daytime TIDs.View full abstractDownload PDF (2211K) -
Kazuo SAITO, Ikuya OTOMO, Toshimitsu TAKAI1991 Volume 43 Issue 11 Pages 921-935
Published: 1991
Released on J-STAGE: September 14, 2010
JOURNAL FREE ACCESSWe newly obtained 38 K-Ar dates for the Tanzawa tonalite and related rocks. The dates for hornblendes in the tonalite as well as that for hornfels adjacent to it indicate that the Tanzawa pluton was formed about 7Ma. Widely distributed 4-5Ma age for biotite could be interpreted as a rapid cooling of the body that started at this time. An 40Ar/39Ar age study suggests that ages older than 10Ma, which were obtained for samples collected in the southwestern part of the body, are due to excess argon in the samples.View full abstractDownload PDF (1712K) -
M. K. TUNÇER, N. OSHIMAN, S. BARIS, Z. KAMACI, M. A. KAYA, A. M ...1991 Volume 43 Issue 11 Pages 937-950
Published: 1991
Released on J-STAGE: September 14, 2010
JOURNAL FREE ACCESSObservations of the geomagnetic total intensity have been carried out from time to time in a possible seismic gap region in the western part of the North Anatolian Fault Zone (NAFZ), in an attempt to trace faultlines through magnetic characteristics and also to relate the characteristics to fault activity. Here we report the results of profile measurements made across the Iznik-Mekece fault as well as our interpretation. The anomalies which we found near Iznik City are similar with the ones that have been found along the eastern part of the Iznik-Mekece fault and hence they could be interpreted in terms of a dike-like structure in the andesite zone adjacent to the fault. In this area the northern edge of the dike-like structure turns out to correspond to the faultline, providing a piece of evidence for the location of faultline. In addition, the dip angle of the dike-like structure provides information on the dip-slip constituent of the primarily right-lateral Iznik-Mekece fault.View full abstractDownload PDF (1218K) -
M. MAKINO, Y. OKUBO, R. MORIJIRI, T. NAKATSUKA, Y. HONKURA1991 Volume 43 Issue 11 Pages 951-956
Published: 1991
Released on J-STAGE: September 14, 2010
JOURNAL FREE ACCESSA blimp-borne survey system was developed to measure the geomagnetic field at low altitude, with a portable proton-precession magnetometer and a portable global positioning system (GPS) installed in a small radio-controlled blimp. The total weight of the instruments was well below the blimp payload of 25kg. The result of the blimp-borne survey which we carried out in the Tanna Basin was compared with that of the ground survey in the same area. It was then confirmed that a magnetic anomaly map could successfully be derived from the blimp survey.View full abstractDownload PDF (2623K)
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