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We review the previously compiled seismic magnitudes for underground nuclear explosions at the Union of the Soviet Socialist Republics Novaya Zemlya Test Site, and analyze these data in the context of published details about individual tests and official Russian reports of annual cumulative explosive energy release at the test site. We derive relationships between teleseismic body wave magnitudem b and explosive yield Y by predicting the yield of each test usingm b and minimizing the difference between predicted and reported annual cumulative yield. A linear relationship between mb and logY with a slope of 0.82 provides a good fit to the annual total yield, with a root mean square (rms) misfit of 0.095 logY units. A spectral magnitude relationship based on the explosion source model of Mueller and Murphy (1971) with a single-free-parameter provides a slightly better fit. For the 10 tests for which individual yields can be directly deduced from the official reports, the rms misfit of reported yields is less than 0.1 logY units or about 25%. More complex relationships that differentiate between the northern and southern test areas, or take account of variations in the scaled depth of burial, do not provide substantially better fits to the reported yields. [ABSTRACT FROM AUTHOR]

We analyzed 18 high-quality waveform doublets with time separations of up to 35 years in the South Sandwich Islands region, for which the seismic signals have traversed the inner core as PKP(DF). The doublets show a consistent temporal change of travel times at up to 58 stations in and near Alaska, and they show a dissimilarity of PKP(DF) coda. Using waveform doublets avoids artifacts of earthquake mislocations and contamination from small-scale heterogeneities. Our results confirm that Earth's inner core is rotating faster than the mantle and crust at about 0.3° to 0.5° per year., The Earth's inner core plays an important role in the geodynamo that generates the Earth's magnetic field, and an electromagnetic torque from the geodynamo is expected to drive the inner [...]

The Earth's inner core's rotational speed, at its equator, is 100,000 times faster than the relative motion of the lithosphere tectonic plates. Estimates of differential rotation of the inner core come from the changes in measurements of the difference in travel time between seismic waves passing through the inner core, and those passing only through the outer core. The anisotropy of the inner core explains the faster propagation of seismic waves that travel closer to the axis of spin. The axis of anisotropy is tilted from the north-south axis by some degrees.

We present a regional short-period Sn magnitude scale mb(Sn) for small earthquakes along the northern Mid-Atlantic Ridge. Surface-wave magnitudes, teleseismic body-wave magnitudes, and seismic moments cannot be reliably determined for small earthquakes along this and other midocean ridges. Local magnitudes that rely on Lg waves are likewise not generally useful due to the substantial oceanic paths for earthquakes along midocean ridges. In contrast, Pn and Sn arrivals for earthquakes along the northern Mid-Atlantic Ridge are generally well recorded by the existing seismographic networks, and, in fact, Sn arrivals are larger than Pn arrivals for about one-third of the ridge events. For this reason, we have developed a new regional Sn magnitude scale that is tied to Mw, so that seismic moments can be readily approximated. In our least-squares fit of peak amplitudes from 120 earthquakes having a published moment magnitude, we solved for the attenuation curve for paths in the oceanic mantle lid, for event magnitude adjustments (EMAs) to account for differences between long-period moment magnitude Mw and short-period Sn magnitude, and for station corrections. We find regional EMAs that are well correlated with the style of faulting: they are positive for normal-faulting earthquakes along spreading ridges and negative for strike-slip earthquakes along transform faults. These source-specific EMAs are approximately +0.11 magnitude units for normal-fault earthquakes and -0.26 magnitude units for strike-slip earthquakes on transform faults, and are consistent with previously reported apparent stresses from these regions. The amplitude distance curve determined for Sn for the northern Atlantic Ocean is similar to that determined for Pn in the northern Atlantic out to a distance of about 500 km, but at larger distances is more similar to the western U.S. Pn curve, likely reflective of the warmer temperatures at greater upper-mantle depths. [ABSTRACT FROM AUTHOR]