ALBERT

Description: Geodetic and seismological characteristics due to a fault movement have been studied on the basis of a simple model. It is intended to examine whether or not such a model is acceptable as a possible representation of earthquake origins. The model is proposed from the standpoint similar to that of Reid's hypothesis and the sudden occurrence of a fracture fault in the upper part of the earth's crust is taken as the immediate cause of earthquake shocks as well as of crustal deformations. First, we deal with statical deformation of the earth's crust caused by stress change (shear) on the fault plane, which is assumed to be developed from the surface vertically down to a certain depth. It has been found that by this model, the general decrease of horizontal displacement of triangulation points with distance from the fault is explained reasonably well. From the comparison of the theory with the observed geodetic data, probable conditions at the actual earthquake fault can be surmised. In the case of the Gômura fault (Tango earthquake), for instance, the depth (H) is estimated at 15km, while the stress change on the fault plane (Yx)0 and the total amount of strain energy (Efault), at 3×107 c.g.s. and 4×1022 ergs, respectively (length of the fault being assumed to be 30 km). Discussion is also made about the characteristics of seismic waves which are generated by the supposed fault movement. The analysis based on a two-dimensional model has shown that the push-pull distribution of the initial P-wave is of the quadrant type, one of the nodal lines coinciding with the fault. The maximum of the spectral intensity (P-wave) falls on the component, whose wave-length (referred to S-wave) is approximately 1.2 times as large as the fault's length. These results also agree satisfactorily well with the observed seismological data. The deduced conditions at the fault are also acceptable judging from the mechanical strength of the crust which is already known. The model adopted here affording satisfactory explanations of various aspects of the Tango earthquake, we might say that the physical conditions at the seismic origin do not differ much from those of the model. Possibility of applying the similar model to other cases is also discussed. © 1958, The Seismological Society of Japan, The Volcanological Society of Japan, The Geodetic Society of Japan. All rights reserved.

Description: Following the end of the Van Allen Probes mission, the Arase satellite offers a unique opportunity to continue in-situ radiation belt and ring current particle measurements into the next solar cycle. In this study we compare spin-averaged flux measurements from the MEPe, HEP-L, HEP-H, and XEP-SSD instruments on Arase with those from the MagEIS and REPT instruments on the Van Allen Probes, calculating Pearson correlation coefficient and the mean ratio of fluxes at L* conjunctions between the spacecraft. Arase and Van Allen Probes measurements show a close agreement over a wide range of energies, observing a similar general evolution of electron flux, as well as average, peak, and minimum values. Measurements from the two missions agree especially well in the 3.6 ≤ L* ≤ 4.4 range where Arase samples similar magnetic latitudes to Van Allen Probes. Arase tends to record higher flux for energies 〈 670 keV with longer decay times after flux enhancements, particularly for L* 〈 3.6 . Conversely, for energies 〉 1.4 MeV, Arase flux measurements are generally lower than those of Van Allen Probes, especially for L* 〉 4.4 . The correlation coefficient values show that the 〉 1.4 MeV flux from both missions are well correlated, indicating a similar general evolution, although flux magnitudes differ. We perform a preliminary intercalibration between the two missions using the mean ratio of the fluxes as an energy- and L*- dependent intercalibration factor. The intercalibration factor improves agreement between the fluxes in the 0.58-1 MeV range.

Description: Measurements of electromagnetic waves in space plasmas are an important tool for our understanding of physical processes in this environment. Inter-calibration of data from different spacecraft missions is necessary for combining their measurements in empirical models or case studies. We show results collected during a close conjunction of the Van Allen Probes and Arase spacecraft. The inter-calibration is based on a fortuitous case of common observations of strong whistlers at frequencies between a few hundred hertz and 10 kHz, which are generated by the same lightning strokes and which propagate along very similar paths to the two spacecraft. Measured amplitudes of the magnetic field fluctuations are the same within ∼14% precision of our analysis, corresponding to 1.2 dB. Currently, archived electric field measurements show twice larger amplitudes on Arase compared to Van Allen Probes but they start to match within ∼33% precision (2.5 dB) once the newest results on the interface of the antennas to the surrounding plasma are included in the calibration procedures. Ray tracing simulations help us to build a consistent scenario of wave propagation to both spacecraft reflected by a successful inter-calibration of the polarization and propagation parameters obtained from multicomponent measurements. We succeed in linking the spacecraft observations to localizations of lightning return strokes by two different ground-based networks which independently verify the correctness of the Universal Time tags of waveform measurements by both spacecraft missions, with an uncertainty better than 10 ms.