Field measurements of absolute gravity in East Antarctica

Abstract This paper reports the results of field-based absolute gravity measurements aimed at detecting gravity change and crustal displacement caused by glacial isostatic adjustment. The project was initiated within the framework of the 53rd Japanese Antarctic Research Expedition （JARE53）. Absolute gravity measurements, together with GPS measurements, were planned at several outcrops along the Prince Olav Coast and S6ya Coast of East Antarctica, including at Syowa Station. Since the icebreaker Shirase （AGB 5003） was unable to moor alongside Syowa Station, operations were somewhat restricted during JARE53. However, despite this setback, we were able to complete measurements at two sites： Syowa Station and Langhovde. The absolute gravity value at the Syowa Station IAGBN （A） site, observed using an FG-5 absolute gravimeter （serial number 210; FG-5 #210）, was 982 524 322.7＋0.1 ktGal, and the gravity change rate at the beginning of 2012 was -0.26 gGal.a-1. An absolute gravity value of 982 535 584.2~0.7 ktGal was obtained using a portable A-10 absolute gravimeter （serial number 017; A-10 #017） at the newly located site AGS01 in Langhovde.     

Without power? Landslide inventories in the face of climate change

Projected scenarios of climate change involve general predictions about the likely changes to the magnitude and frequency of landslides, particularly as a consequence of altered precipitation and temperature regimes. Whether such landslide response to contemporary or past climate change may be captured in differing scaling statistics of landslide size distributions and the erosion rates derived thereof remains debated. We test this notion with simple Monte Carlo and bootstrap simulations of statistical models commonly used to characterize empirical landslide size distributions. Our results show that significant changes to total volumes contained in such inventories may be masked by statistically indistinguishable scaling parameters, critically depending on, among others, the size of the largest of landslides recorded. Conversely, comparable model parameter values may obscure significant, i.e. more than twofold, changes to landslide occurrence, and thus inferred rates of hillslope denudation and sediment delivery to drainage networks. A time series of some of Earth's largest mass movements reveals clustering near and partly before the last glacial‐interglacial transition and a distinct step‐over from white noise to temporal clustering around this period. However, elucidating whether this is a distinct signal of first‐order climate‐change impact on slope stability or simply coincides with a transition from short‐term statistical noise to long‐term steady‐state conditions remains an important research challenge. Copyright © 2011 John Wiley & Sons, Ltd.     

Interpretation in terms of gyrotropic waves of Schumann-resonance-like line emissions observed at Nakatsugawa in possible association with nearby Japanese earthquakes

The observation of ULF/ELF electromagnetic waves in the frequency range below 50 Hz has been continued at Nakatsugawa (in the Gifu prefecture), Japan since 1998. This paper summarizes anomalous Schumann resonance (SR) phenomena and SR-like line emissions observed at Nakatsugawa in possible association with recent nearby earthquakes (EQs) (the 2004 Mid-Niigata prefecture and the 2007 Noto-Hanto (peninsula) EQs), which have been already described in detail by Ohta et al. (2009). The intensity of particular modes of SR increased before these large EQs and the excitation of other anomalous SR-like line emissions also existed at the frequency shifted by about 2 Hz from the typical SR modes. Since temporal changes of the anomalous SR modes and line emissions are synchronous in time, there might be a possibility that the line emission is a consequence of the anomalous SR. In this paper we propose an interpretation of those anomalous phenomena in terms of excitation of gyrotropic waves due to input wave from below with a band from 15 to 20 Hz as an exciter. The theoretical computational results seem to be generally consistent with the observational finding.     

Development of Long-period Ground Motions from the Nankai Trough, Japan, Earthquakes: Observations and Computer Simulation of the 1944 Tonankai (Mw 8.1) and the 2004 SE Off-Kii Peninsula (Mw 7.4) Earthquakes

Strong ground motions recorded in central Tokyo during the 1944 Tonankai Mw8.1 earthquake occurring in the Nankai Trough demonstrate significant developments of very large (>10 cm) and prolonged (>10 min) shaking of long-period (T > 10–12 s) ground motions in the basin of Tokyo located over 400 km from the epicenter. In order to understand the process by which such long-period ground motions developed in central Tokyo and to mitigate possible future disasters arising from large earthquakes in the Nankai Trough, we analyzed waveform data from a dense nation wide strong-motion network (K-NET and KiK-net) deployed across Japan for the recent SE Off-Kii Peninsula (Mw 7.4) earthquake of 5 September 2004 that occurred in the Nankai Trough. The observational data and a corresponding computer simulation for the earthquake clearly demonstrate that such long-period ground motion is primarily developed as the wave propagating along the Nankai Trough due to the amplification and directional guidance of long-period surface waves within a thick sedimentary layer overlaid upon the shallowly descending Philippine Sea Plate below the Japanese Island. Then the significant resonance of the seismic waves within the thick cover of sedimentary rocks of the Kanto Basin developed large and prolonged long-period motions in the center of Tokyo. The simulation results and observed seismograms are in good agreement in terms of the main features of the long-period ground motions. Accordingly, we consider that the simulation model is capable of predicting the long-period ground motions that are expected to occur during future Nankai Trough M 8 earthquakes.     

Comparison of time delays of sprites induced by winter lightning flashes in the Japan Sea with those in the Pacific Ocean

The measurement of unusual winter sprites in the Hokuriku area (Japan Sea side) was performed as a primary target of the 2006/2007 winter campaign by means of coordinated optical and extremely low frequency (ELF)/very high-frequency (VHF) electromagnetic observations. We have also added the same observations for the sprites in the Pacific Ocean, to be compared with the characteristics of Hokuriku sprites. The following results have emerged from this campaign: (i) the predominance of column sprites in winter has been confirmed not only for the Hokuriku area but also in the Pacific Ocean (with the probability just above 60%), (ii) carrots are much more frequently observed in the Pacific Ocean (with a probability of ～28%) than in the Hokuriku area (～16%), (iii) a very unique property of Hokuriku sprites is the surprisingly long delay (average ～90 ms) of sprites from their parent lightning flashes and the delays for carrots and columns exhibit some significant difference (80 ms for columns and 100 ms for carrots) and (iv) the time delay of Pacific Ocean sprites is much shorter (～43 ms average) than that at Hokuriku, but there is no remarkable difference in delay between carrots and columns. Finally we discussed the importance of time delay studies to understand sprite generations and their parent lightning discharges, because the difference of time delays on the Japan Sea side and in the Pacific Ocean are thought to be causally related to the parameters of parent thunderstorms.     

Understanding Amazonian fluvial rias based on a Late Pleistocene–Holocene analog

Fluvial rias are elongated lakes at tributary mouths that can reach dozens of kilometers in length, constituting one of the most remarkable features in the Amazonian landscape. Thus far, definitive data which documents the genesis of fluvial rias have not been published. The main goal of this work was to integrate morphological, sedimentological and chronological information in order to characterize fluvial paleorias in the interfluve of the Purus and Madeira Rivers and discuss the most likely hypothesis for their genesis. These paleorias were first observed through remote sensing imagery as several elongated and interconnecting belts of open vegetation that are in sharp contact with the surrounding dense forest. The belts are branched and form a dendritic pattern similar to many modern drainage networks. The sedimentary record of these belts revealed the prevalence of sharp‐based sandstones and mudstones arranged into fining‐upward successions, which are compatible with deposition within channels. Active channel and abandoned channel deposits were recognized. These are topped by continuous mudstones related to rapid channel abandonment and formation of a low energy basin or ria environment. Radiocarbon dating of these deposits recorded only Late Pleistocene and Holocene ages ranging from 21 547–22 285 cal yr bp to 5928–6124 cal yr bp . This chronology for sediment deposition is not compatible with the hypothesis of Amazonian rias being formed by fluvial erosion during the Last Glaciation Maximum low sea level, with sediment accumulation during the subsequent Holocene transgression. Instead, the studied paleorias record previous tributaries of the Madeira River that became abandoned as the position of this river shifted southeastward and its interfluve tilted northward, inverting the drainage systems. Therefore, a neotectonic origin of some Amazonian paleorias seems most likely. This hypothesis should be considered in further investigations aiming at understanding the origin of numerous modern fluvial rias that typify the Amazonian landscape. Copyright © 2014 John Wiley & Sons, Ltd.     

Equatorial field-aligned irregularities deduced from the echo-train and hybrid whistlers

Summary Equatorial field-aligned irregularities have been studied by using low-latitude echotrain and hybrid whistlers observed at Sakushima Station (geomag. lat. 24°). The structure is discussed in relation to the propagation mode trapped by field-aligned irregularities. We then find that the field-aligned irregularities responsible for the trapping of low latitude whistlers are of such small dimension as the HF ducts.     

Electromagnetic anomalies associated with 1995 Kobe earthquake

Occurrences of anomalous electro-magnetic phenomena at varied frequency ranges, covering ELF to VHF, have been reported in relation to the 17 January 1995 Kobe earthquake (M7.2), by several independent research groups. Prominent pre-seismic peaks, which could have been emitted from the focal area, were observed on 9-10 January in ELF, VLF, LF and HF ranges. Whether these changes were truly related to the earthquake is not certain, because atmospheric (thunderbolt discharge) activities also peaked on 9-10 January. The nomalous changes were markedly enhanced toward the catastrophe in agreement with many reports on unusual radio/TV noise. Anomalous transmission of man-made electromagnetic waves in VLF and VHF ranges was also detected from a few days before the earthquake, indicating the possibility that the ionosphere above the focal zone was disturbed at the final stage of the earthquake preparation process.     

Iron K-emission line from Cygnus X-2

The iron K-emission line of Cyg X-2 was detected from the TENMA observation. The centre energy, the equivalent width and the intrinsic line width are 6.7 keV, 30 eV, and less than 0.6 keV, respectively. These properties indicate that the observed line is mostly due to helium-like iron and the electron scattering depth of the line emitting region is smaller than three.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.