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Several statistical tests were used to investigate the possibility that the earthquakes in the Swabian Jura are triggered by the tidal stress in the Earth. The results provide weak evidence that the earthquakes tend to occur when the tidal shear stress on the fault plane in the direction supporting the tectonic stress is greatest. A comparison of some of the statistical methods available for investigating tidal triggering effects is made.
ARK: https://n2t.net/ark:/88439/y090017
Permalink: https://geophysicsjournal.com/article/41
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Estimates of Q of mode oSo as measured after the Chilean (1960) and Alaskan (1964) earthquakes showed large scatter. The Indonesian quake of August 19, 1977, has provided a new opportunity to determine the attenuation factor for oSo. Time lapse spectra of a priori selected high quality data were analyzed using a maximum-likelihood method and Ricean statistics. Data from South Pole and Los Angeles gave Q values of 6324 (1 ±21 %) and 6859 (1 ± 17%) respectively. Taken together the result is 6687 (1 ± 13%).
ARK: https://n2t.net/ark:/88439/y084078
Permalink: https://geophysicsjournal.com/article/39
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During METEOR cruise 45 in August 1977 14 heat flow measurements were obtained along a profile east of the Reykjanes Ridge and perpendicular to the ridge axis covering a distance range from 30 to 240 km. Closely spaced measurements were grouped together. The mean heat flow of all groups amounts to 109±20 mW m-2. The values do not reveal a distinct increase with decreasing distance from the ridge axis as may be expected from the theoretical heat flow distribution based upon a cooling plate model. Including earlier measurements a high and very uniform heat flow in the distance range from 170 to 340 km was observed with a mean value of about 100 mW m-2. In order to explain this high heat flow a temperature of 930° C is required at the lower boundary of the lithosphere at a depth of 50 km, assuming a purely conductive heat transport. Compared with the results obtained from previous measurements west of the Reykjanes Ridge, the data reveal an asymmetric thermal behaviour of the ridge area. The average heat flow east of the ridge amounts to 93 mW m-2 being nearly twice the heat flow of the region west of the ridge.
ARK: https://n2t.net/ark:/88439/y073309
Permalink: https://geophysicsjournal.com/article/37
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Mode 0S0 was excited by the Indonesian earthquake of 19 August 1977 and recorded at the South Pole and at UCLA. Phase estimates from 16 independent time lapse spectra were used to determine the frequency of this mode to high precision. The result is f (0S0) = 2.932851 cph with a standard deviation of 11 ppm.
ARK: https://n2t.net/ark:/88439/y062410
Notes: Erratum
Permalink: https://geophysicsjournal.com/article/36
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From the recognition of common apparent polar-wander (CAPW) paths for Africa, Australia, Greenland, and North America in the early Proterozoic, we have deduced that these continents today occupy approximately the same relative locations on the globe as they did in the early Proterozoic. However, there is abundant geochemical, geological, geochronological and tectonic evidence for landmasses having been much less dispersed in the Precambrian than they are now. It is shown in this paper that an Earth of about half the present radius accomodates the present continents in such a manner that this paradox can be satisfactorily resolved, and we propose that between about 1,600 Myr and 1,000 Myr ago, the Earth expanded to approximately its present dimensions. A change from Proterozoic to Phanerozoic tectonic styles is supported.
ARK: https://n2t.net/ark:/88439/y034403
Permalink: https://geophysicsjournal.com/article/34
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The full range of 72h-forced, 72 superharmonic resonance periods, is detected in time-series of all 866 earthquakes of (robust averages of) Mw5.6+ from USGS, EMSC, and GFZ, 2015-2019 catalogs. The resonance is in the 55’–15 days long-periodic band (0.303 mHz–0.771605 μHz) at 99–67% confidence. Moreover, omitting of the 21 overrepresenting events has improved the result. The signal is clear, strong, and stable – demonstrating beyond doubt that Mw6.2+ seismicity arises due to long-periodic resonance. Remarkably, the natural mode’s cluster was detected too; it averaged 60.1’, while the overall strongest resonance period was also 59.9’, at 2.3 var%, or to within the 1Hz sampling rate – revealing that the 72 h forcer is the modulator of the Earth’s natural period via synchronization. The dominance property of the forcer also follows from detection of its many other fractional multiples: 14/5, 3/2, 5/12, 5/36, etc. After Schumann resonance discovery in the short band (extremely long band of the EM Spectrum), this is the second report ever of a full resonance bundle in any global data, and the first ever in tectonic earthquakes occurrences. The Mw6.2+ seismotectonics arises via resonance-rupture response of tectonic plates and regions to the resonant phase or its fractional multiples. Fundamental questions of geophysics including earthquake prediction can be solved if the Earth is taken to be a multi-oscillator nonlinear system. As an immediate benefit, the find enables a reliable partial seismic anti-forecasting (prediction of seismic quiescence), months ahead globally. This discovery of mechanically induced extreme-band energy on Earth invalidates the main (heat-transfer) geophysical hypothesis and thus should drastically diminish the role of chemistry in geosciences, specifically of geochemistry.
ARK: https://n2t.net/ark:/88439/x020219
Permalink: https://geophysicsjournal.com/article/31
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DOI:10.5281/2646487 | online first: 18 Apr 2019 CERN
Moon body resonance, 63(1):30-42
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On 8 June 2008 at 12:25 GMT, a large (Mw6.4) earthquake occurred NE of the town of Andravida in Western Peloponnese, Greece – an area characterized by high seismicity during the last decade. In this study, the local velocity structure of the Andravida Fault Zone (AFZ) is investigated primarily using data recorded during the period 2012-2017 by the Hellenic Unified Seismological Network (HUSN). We selected about 1,500 seismic events recorded by the local HUSN stations as well as the Hellenic Strong-Motion Network (HSMN). By applying tomographic inversion, we produced and interpreted 3D models of VP, VS, and VP/VS ratio in the study area. The spatial distribution of the aftershocks, as well as the 3D model derived by Local Earthquake Tomography (LET), provided evidence for the rupture plane. Surface breaks and minor faults are found to be oblique to the main direction of the AFZ, as a result of a restraining bend in Mtn. Movri and the formation of a positive flower-structure in the shallow layers of the upper crust.
ARK: https://n2t.net/ark:/88439/x014750
Permalink: https://geophysicsjournal.com/article/29
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We examine the general non-linear inverse problem with a finite number of parameters. In order to permit the incorporation of any a priori information about parameters and any distribution of data (not only of gaussian type) we propose to formulate the problem not using single quantities (such as bounds, means, etc.) but using probability density functions for data and parameters. We also want our formulation to allow for the incorporation of theoretical errors, i.e. non-exact theoretical relationships between data and parameters (due to discretization, or incomplete theoretical knowledge); to do that in a natural way we propose to define general theoretical relationships also as probability density functions. We show then that the inverse problem may be formulated as a problem of combination of information: the experimental information about data, the a priori information about parameters, and the theoretical information. With this approach, the general solution of the non-linear inverse problem is unique and consistent (solving the same problem, with the same data, but with a different system of parameters does not change the solution).
ARK: https://n2t.net/ark:/88439/y048722
Permalink: https://geophysicsjournal.com/article/28
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Broadband recordings from the GRF (Grafenberg) Array of the strongest earthquakes from Greece are examined. A P-wave seismogram section of a number of events in the range between 1,300 and 2,100 km epicentral distance is constructed. The dominant feature in this section is the second arrival, which is the reflection from the 400 km discontinuity. Characteristic amplitude changes of this phase across the array are observed. The apparent velocity across the array of the first arriving P phase is very slow, indicating a slower upper mantle in SE Europe than in other regions. There is also a very weak indication of a third phase. The resulting model of the upper mantle, which was derived with the aid of theoretical seismograms, shows a pronounced discontinuity at a depth of 400 km. The time difference between the observed first two phases can be used for a fast estimation of the epicentral distance.
ARK: https://n2t.net/ark:/88439/y035633
Permalink: https://geophysicsjournal.com/article/19
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We report on a 40Ar–39Ar study of hornblende, biotite, and glass samples from the Nordlinger Ries impact crater. The samples are derived from various depths (377–1,200 m) of the Forschungsbohrung 1973 drill core, from the ejecta blanket, and the crystalline crater rim. All mineral separates display 40Ar–39Ar plateau ages of 320 ± 3 m.y. The data represent the first direct age determination of the Ries bedrock. The plateau ages of suevite and moldavite, both generated in the Ries impact, date the cratering event which occurred 15 m.y. ago. The results from the mineral separates imply that shock pressure alone, even as high as 450 kbar, cannot reset K–Ar ages of hornblende and biotite. This result is significant for the interpretation of ages of impact breccias in general, and for the interpretation of lunar highland rock ages in particular. 40Ar–39Ar studies yield, as a side result, data on the natural loss of radiogenic 40Ar. In this report we emphasize on this aspect to estimate the cooling history of the suevite layer. We compare the measured 40Ar-loss to the loss calculated from a simple cooling model of the layer and from the diffusion properties of the minerals as obtained in the stepwise heating experiment. The resulting upper limit for the post-shock equilibrium temperature within the suevite layer is 450°C.
ARK: https://n2t.net/ark:/88439/y028544
Permalink: https://geophysicsjournal.com/article/18
