Geofisica pura e applicata

The problem of the gross nature of the Jovian atmospheric circulation is examined from the viewpoint of the following previous findings of the writer and others. 1) The equatorial acceleration cannot be accounted for by axisymmetric motions. 2) The departures from symmetry in a rotating system having an equatorial acceleration must impart angular momentum selectively to those particles moving toward the jet maximum and abstract it from those moving away. 3) These selective (pressure) torques and associated sorting processes arise spontaneously in the presence of a vertical convection mode involving motions not independent of longitude, if the cell sizes and other conditions are right. Since there is evidence that Jovian dark spots have statistical maxima of occurrence along the tropical shear lines flanking the equator, these are assumed to be vertical convective systems forming, in effect,convective vortex sheets which generate the high angular momentum of the equatorial zone. Various additional concepts are discussed, and many comparisons with conditions in the sun and in the earth's atmosphere are made.

—We investigate the deep subsurface structure below the artificial reservoir at the Soultz Hot Dry Rock (HDR) site in France by a reflection method which uses acoustic emission (AE) as a wave source. In this method, we can detect reflected waves by examining the linearity of a three-dimensional hodogram. Additionally for imaging a deep subsurface structure, we employ a three-dimensional inversion with a restriction of wave polarization angles and with a compensation for a heterogeneous source distribution.¶We analyzed 101 AE wave forms observed at the Soultz site during the hydraulic testing in 1993. Some deep reflectors were revealed by this method. The bottom of the artificial reservoir that is presumed from all of the AE locations in 1993 was delineated at the depth of about 3900 m as a reflector. Other deeper reflectors were detected below the reservoir, which would not have been detected using conventional methods. Furthermore these reflectors agreed with the results of the tri-axial drill-bit VSP (Asanuma et al., 1996).

The magnetotelluric method relies on variations of natural electromagnetic fields, which in the vicinity of human settlements are persistently distorted by anthropogenic electromagnetic noise. A large source of noise to the magnetotelluric response is caused by the harmonic oscillations of the power network utility frequency centered on 50/60 Hz along with the associated higher harmonics. Removing this type of noise is essential for high frequency magnetotelluric measurements used for shallow surveys. There are a large number of approaches for how to treat power line noise in magnetotelluric signals, however, commonly used methods do not take into account time variations/instabilities of the utility frequency. That is not serious problem in vicinity of well balanced grid networks, but can cause issues in regions with larger utility frequency variations. Under such conditions, commonly used methods loose more of the natural signal, which is undesirable especially in case of very noisy datasets. Hence, we adopted approach for removing of power line noise with respect to time variations of the utility frequency and applied it to magnetotelluric signals to preserve more of natural signal. The method is based on modelling of the grid network harmonic oscillations by the optimum utility frequency and its integer multiples. The resulting sum of sinusoidal signals is subsequently subtracted from recorded data and only particular noise frequencies are removed from the original signal with high precision, while frequency ranges around power line harmonics are cleaned.

The attenuation characteristics around Bilaspur region of the Himachal Lesser Himalaya have been estimated adopting extended-coda-normalization method, and using a data set of 41 local events (0.5 < M L ≤ 2.9) that occurred in the region from May 2013 to March 2014. The frequency-dependent relations governing the quality factors of P-waves (Q α ) and S-waves (Q β ) in the frequency range from 1.5 to 24 Hz are: (Q α ) = (43 ± 4) f 1.30±0.04 and Q β  = (79 ± 6) f 1.25±0.02. The average estimates of (Q α ) and (Q β ) are found to vary from 71 and 125 at 1.5 Hz to 2901 and 4243 at 24 Hz, respectively. The (Q α ) and (Q β ) estimates are compared to the similar estimates obtained for the other seismically active regions of the Himalaya. It is found that for the various Himalayan regions, the (Q α ) estimates at 1 Hz vary between 22 (for the Kumaon Himalaya) and 97 (for the northwest Himalaya), whereas (Q β ) estimates range between 63 (for the Garhwal Himalaya) and 127 (for the northwest Himalaya). For the Bilaspur region, the (Q β )/(Q α ) ratio is greater than unity and varies between 1.84 and 1.45 in the frequency range from 1 to 24 Hz. The region-specific attenuation relations can be adopted for estimating earthquake source parameters, simulating strong ground motion and assessing seismic hazard for the Bilaspur region of Himachal Lesser Himalaya.

The stability properties of the nongeostrophic disturbances are studied in a barotropic zonal current. The growth rate of the nongeostrophic disturbances is increased and the instability is generally shifted towards shorter wavelengths. Even in the structure of the nongeostrophic disturbances large differences are found as compared to geostrophic disturbances.

Submarine cables are a typical weak magnetic target. Studying the magnetic anomaly principle of these cables and establishing their magnetic anomaly model are the bases of realizing magnetic detection, location, and recognition. The magnetic anomaly model of a 2D, infinite-length, horizontal cylinder is traditional and typical. However, when the cable is laid on a polygonal line under the constraints of geographical conditions or it is broken, the traditional model is no longer applicable. In this study, a magnetic anomaly analysis model of a finite-length submarine cable was proposed based on magnetic anomaly theory of finite-length horizontal cylindrical shells. The characteristics, applicability, and magnetic anomaly variation law of the model were analyzed. Exploration of the critical length ratios for the magnetic anomaly of a finite-length submarine cable that cannot be calculated by the traditional model improves the present magnetic anomaly theory of submarine cables.