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Earth, planets and space
published for the Society of Geomagnetism and Earth, Planetary, and Space Sciences (SGEPSS), the Seismological Society of Japan, the Volcanological Society of Japan, the Geodetic Society of Japan, the Japanese Society for Planetary Sciences by Terra Scientific Publishing Company (TERRAPUB)
Earth, planets and space

published for the Society of Geomagnetism and Earth, Planetary, and Space Sciences (SGEPSS), the Seismological Society of Japan, the Volcanological Society of Japan, the Geodetic Society of Japan, the Japanese Society for Planetary Sciences by Terra Scientific Publishing Company (TERRAPUB)

1343-8832

Earth, planets and space/Journal Earth, planets and space
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收录年代

    Contemporary horizontal crustal movement estimation for northwestern Vietnam inferred from repeated GPS measurements

    Takeshi SagiyaFumiaki KimataDuong Chi CongNguyen Anh Duong...
    12页
    查看更多>>摘要：We present a horizontal velocity field determined from a GPS network with 22 sites surveyed from 2001 to 2012 in northwestern Vietnam. The velocity is accurately estimated at each site by fitting a linear trend to each coordinate time series, after accounting for coseismic displacements caused by the 2004 Sumatra and the 2011 Tohoku earthquakes using static fault models. Considering the coseismic effects of the earthquakes, the motion of northwestern Vietnam is 34.3 ± 0.7 mm/yr at an azimuth of N108? ± 0.7?E in ITRF2008. This motion is close to, but slightly different from, that of the South China block. The area is in a transition zone between this block, the Sundaland block, and the Baoshan sub-block. At the local scale, a detailed estimation of the crustal deformation across major fault zones is geodetically revealed for the first time. We identify a locking depth of 15.3 ± 9.8 km with an accumulating left-lateral slip rate of 1.8 ± 0.3 mm/yr for the Dien Bien Phu fault, and a shallow locking depth with a right-lateral slip rate of 1.0 ± 0.6 mm/yr for the Son La and Da River faults.
      原文链接:
    • NSTL
    • Springer Nature

    Dynamic tsunami generation due to sea-bottom deformation: Analytical representation based on linear potential theory

    Tatsuhiko Saito
    13页
    查看更多>>摘要：Recording ocean-bottom pressures in offshore regions has increased our understanding of tsunami sources and promoted the development of rapid source estimation for early tsunami warning. Analytical solutions for the water height at the surface have often played an important role as a reference model in these efforts. To understand the system better and to develop the techniques further, not only the water height but the velocity in the sea and the pressure at the sea bottom are important. The present study obtains a solution for the velocity potential for sea-bottom deformation with an arbitrary source time function, and derives analytical solutions for the velocity distributions in the sea and the pressure at the bottom. These enable us to visualize the tsunami generation process, including the velocity field. The solutions can also give a theoretical background for setting the initial conditions of height and velocity in 2-D tsunami propagation simulations. Furthermore, the solution of the ocean-bottom pressure indicates that when the sea-bottom uplifts at an increasing rate, the sea-bottom pressure increases through a dynamic effect. This dynamic contribution will not be negligible as we develop more rapid and precise source estimation techniques using ocean-bottom pressure gauges within the source region.
      原文链接:
    • NSTL
    • Springer Nature

    Simulations of P-SV wave scattering due to cracks by the 2-D finite difference method

    Yuji SuzukiTakahiro ShiinaJun KawaharaTaro Okamoto...
    15页
    查看更多>>摘要：We simulate P-SV wave scattering by 2-D parallel cracks using the finite difference method (FDM). Here, special emphasis is put on simplicity; we apply a standard FDM (second-order velocity-stress scheme with a staggered grid) to media including traction-free, infinitesimally thin cracks, which are expressed in a simple manner. As an accuracy test of the present method, we calculate the displacement discontinuity along an isolated crack caused by harmonic waves using the method, which is compared with the corresponding results based on a reliable boundary integral equation method. The test resultantly indicates that the present method yields sufficient accuracy. As an application of this method, we also simulate wave propagation in media with randomly distributed cracks. We experimentally determine the attenuation and velocity dispersion induced by scattering from the synthetic seismograms, using a waveform averaging technique. It is shown that the results are well explained by a theory based on the Foldy approximation, if the crack density is sufficiently low. The theory appears valid with a crack density up to at least 0.1 for SV wave incidence, whereas the validity limit appears lower for P wave incidence.
      原文链接:
    • NSTL
    • Springer Nature

    Fault plane of the 1964 Niigata earthquake, Japan, derived from relocation of the mainshock and aftershocks by using the modified joint hypocenter determination and grid search methods

    Nobuo HurukawaTomoya Harada
    7页
    查看更多>>摘要：We relocated the mainshock and immediate aftershocks of the 1964 Niigata earthquake (M_s 7.5) using both the modified joint hypocenter determination (MJHD), and the grid search (GS), methods to obtain their hypocenters and identify the fault plane of the mainshock. We used P-wave arrival times at 13 Japanese stations reported by the Japan Meteorological Agency (JMA). Firstly, we performed the MJHD method to select readings with high accuracies and to obtain station corrections that related to the lateral heterogeneity of the Earth's structure. Secondly, we performed the GS method by using only selected readings and assuming the station corrections. Based on the relocated hypocenters, we found that the mainshock and immediate aftershocks occurred along a plane striking N15?E and dipping 11? eastward. This result strongly suggests that one of the nodal planes of the mainshock, for which the strike and dip are N9?E and 34?, respectively, is preferable as the fault plane. When global stations are also used for relocations, the results confirm that the fault plane of the 1964 Niigata earthquake dips gently eastward. Therefore, we concluded that the fault plane of the 1964 Niigata earthquake is gently eastward-dipping.
      原文链接:
    • NSTL
    • Springer Nature

    Examination of source fault model for the Gifu-Ichinomiya fault based on seismic intensity data

    Masayuki KuriyamaHiroaki SatoTomotaka Iwata
    14页
    查看更多>>摘要：To investigate possible source fault models for the Gifu-Ichinomiya fault, we construct multiple source fault models of the 1891 Nobi earthquake, taking into account several different types of geometry for the Gifu- Ichinomiya fault, and conduct strong ground motion simulations. We choose the most plausible source model by comparing the distribution of simulated seismic intensities with the spatial distribution of a questionnairebased intensity of 7, and with that of the damage ratio of wooden houses in the near-source region. Our results imply that the length of the source fault of the Gifu-Ichinomiya fault is relatively short and the dip angle is 75 degrees to the east. Because a seismic intensity of 7 is considered to arise from site amplification and the short distance from a source fault, we classified the points with a seismic intensity of 7 based on the H/V spectral ratio of microtremors by considering the contributing factors to the generation of a seismic intensity of 7. A linear distribution of the points, which might have relatively lower site amplification factors, in the northeastern part of the Nobi Plain implies that a part of the source fault of the 1891 Nobi earthquake existed in this area, as indicated through strong ground motion simulations.
      原文链接:
    • NSTL
    • Springer Nature

    Seismic quiescence and activation anomalies from 2005 to 2008 beneath the Kanto district, central Honshu, Japan

    Shin'ichi SakaiKei Katsumata
    13页
    查看更多>>摘要：In the present study, an earthquake catalog is used that lists 1,197 earthquakes with M ≥ 3.9. All of the earthquake waveforms were recorded by the Earthquake Research Institute, University of Tokyo. These waveforms have been manually re-examined, and hypocenters and magnitudes re-calculated. A detailed analysis of the re-determined earthquake catalog between 1996 and 2007, using a gridding technique (ZMAP), shows a pair of seismic quiescence and activation anomalies that start around the middle of 2005, and last about 30 months. The pair of quiescence and activation anomalies are located very close to each other, and the Z-values are +5.0 and ?3.8 for a time window of T_w = 1.5 years, using a sample size of N = 100 earthquakes. The anomaly pair is not a coincidence as is confirmed by a numerical simulation with the assumption of random seismicity. One possible hypothesis is presented to explain the seismicity anomaly: a long-term slow slip event (LSSE) occurs on the upper boundary of the subducting Pacific plate, and the seismic quiescence and activation anomalies are caused by the Coulomb failure stress change associated with the LSSE.
      原文链接:
    • NSTL
    • Springer Nature

    Volcano inflation prior to an eruption: Numerical simulations based on a 1-D magma flow model in an open conduit

    Ryohei KawaguchiTakeshi NishimuraHaruo Sato
    13页
    查看更多>>摘要：We numerically simulate volcanic inflation caused by magma ascent in a shallow conduit at volcanoes which repeatedly erupt, in order to understand the effect of volatile behavior on magma from geodetic data. Considering magma in which the relative velocities between melt and gas bubbles are negligible, we model magma flow in a one-dimensional open conduit with diffusive gas bubble growth. We calculate the ground displacements and tilts caused by spatio-temporal changes of magma pressure in the conduit. Our simulations show that magma without volatiles causes decelerated changes in volcanic inflation. Magma with gas bubble growth inflates the volcano with a constant, or accelerated, rate. Temporal changes of volcanic deformation are also affected by the magma pressure at the bottom of the conduit. When the pressure is small, the displacements and tilts increase in proportion to the 1.5th power of time. This time rate is similar to that predicted from a basic gas bubble growth model. When the pressure equals the lithostatic pressure, the effects of gas bubble growth relatively decrease and the displacements and tilts increase linearly with time.
      原文链接:
    • NSTL
    • Springer Nature

    Subtle changes in strain prior to sub-Plinian eruptions recorded by vault-housed extensometers during the 2011 activity at Shinmoe-dake, Kirishima volcano, Japan

    Ken'ichi YamazakiMasahiro TeraishiKazuhiro IshiharaShintaro Komatsu...
    9页
    查看更多>>摘要：This study focuses on strain change observations with a precision of 10~(?9) associated with the 2011 Shinmoedake eruptions in Japan, using vault-housed extensometers installed approximately 18 km northwest of the Shinmoe-dake crater. The extensometers recorded major strain changes of 10~(?7) during three sub-Plinian eruptions and subsequent magma effusion. Our analysis indicates that these extensometer records provide a reasonable estimation of the parameters of an isotropic point source that can explain eruption-related ground deformation. The extensometers also recorded subtle strain changes of 10~(?9) prior to the three sub-Plinian eruptions. Time series data indicate that changes in strain at these rates are generally only observed immediately before explosive eruptions, suggesting that these strain changes are precursors to sub-Plinian eruptions. The source of these subtle strain changes is likely to be shallower than the magma chamber associated with these eruptions. The precursory strain changes might have been caused by a pressure increase and a subsequent pressure decrease under the volcano. One possible scenario that can explain these pressure changes is the accumulation of volcanic gases at depth, causing an increase in pressure that was eventually released during gas emissions from the crater prior to the explosive eruptions.
      原文链接:
    • NSTL
    • Springer Nature

    Paleointensity determination of Late Cretaceous basalts in northwest South Korea: implications for low and stable paleofield strength in the Late Cretaceous

    Seong-Jae DohYongjae YuWonnyon KimBongsu Chang...
    13页
    查看更多>>摘要：To clarify geomagnetic field behavior in the Late Cretaceous, paleointensity and rock-magnetic studies were carried out on basalts with K-Ar ages of 78.6 ± 2.5 and 73.1 ± 1.6 Ma in northwest South Korea. A total of 314 samples (262 from six lava flows and 52 from massive basalts) were subjected to Thellier-type IZZI paleointensity experiments. Through the application of seven paleointensity selection criteria that mainly verify the thermal alteration of magnetic minerals and the stability of remanence direction, fifteen paleointensity data were obtained from five of the lava flows. Based on rock-magnetic experiments and microscopic observations, it is revealed that the measured paleointensity is carried by single-domain (titano)magnetite. The site-mean paleointensities ranged 13.1-21.3 μT, which corresponds to a virtual axial dipole moment of 2.3-3.8 × 10~(22) Am~2. The combination of this result with selected data from the IAGA paleointensity database establishes the existence of different dipole moments according to rock type. In particular, the geomagnetic field strength recorded in Late Cretaceous crystalline volcanic rock was relatively low and stable, with a mean dipole moment of 4.0 ± 1.9 × 10~(22) Am~2 regardless of geomagnetic field reversals.
      原文链接:
    • NSTL
    • Springer Nature

    Secular trend of geomagnetic elements in the Indian region

    S. K. BhardwajP. B. V. Subba Rao
    9页
    查看更多>>摘要：In the present study, secular trends and jerks in the geomagnetic elements D, H and Z are investigated at the six Indian magnetic observatories using annual and monthly mean values for all days, quiet days and night base (night time mean). The residuals of all-day annual and monthly means are computed by removing a polynomial fit from their best fitting curves. The residuals of D, H and Z curves do not show any parallelism with the 11-year sunspot cycle. At Alibag, the D residual shows a periodicity of 2 solar cycles, whereas the H and Z residuals indicate a quasi-periodicity of 3 solar cycles for the period 1921-2009. At the Indian stations, an in-phase solar cycle component is observed for 2 of the solar cycles in the D and Z residuals, while the H residual shows outof- phase variations with the sunspot cycle for the period 1958-2009. Two geomagnetic jerks, 1970 and 1991, are well reflected in the monthly and annual mean values in the Indian region, as observed globally.
      原文链接:
    • NSTL
    • Terra Scientific Publ Co