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Short‐period, three‐component recordings of the seismic wave field of Peaceful Nuclear Explosions (PNEs) on long‐range profiles are used to determine the fine structure of the mantle lithosphere. By analyzing the frequency content of the recorded phases and applying different band‐pass filters to the data, it is possible to divide the wave field into two distinctly different constituents: low‐frequency body waves traveling along Fermat paths (first arrivals) and the high‐frequency teleseismic (or long‐range) Pn phase traveling with a group velocity of 8.1 km/s and accompanied by a long, incoherent coda. This high‐frequency teleseismic Pn phase is observable from about 750 km, where it separates from the faster first arrival, to the maximum recording distance of 3145 km. It is recorded from shots at different locations and appears to be almost unaffected by the major tectonic feature along the profile, the Urals. The frequency spectrum of this Pn phase contains more high‐frequency energy (up to 12 Hz) than first arrivals that penetrate deeper into the upper mantle. The teleseismic high‐frequency Pn arrival has a remarkable coda, which is incoherent between closely spaced stations. The coda duration is dependent on the component of motion, being shortest on the vertical and longest on the transverse component. We propose a velocity model that is characterized by a zone extending from the crust‐mantle boundary to a depth of about 100 km. This zone has randomly distributed, spatially anisotropic velocity fluctuations. We propose that these velocity heterogeneities are “stretched” in the horizontal direction. This zone forms a scattering waveguide that confines the high‐frequency teleseismic Pn. There are indications that below this Pn waveguide, either the scale of the velocity fluctuations or the Q factor changes. This is expressed in a separation of the teleseismic Pn phase from the phase diving deeper into the mantle lithosphere.

Abstract. Short-period, three-component recordings of peaceful nuclear explosions (PNEs) in northern Eurasia are used to constrain the P wave velocity structure of the mantle transition zone. The properties of the upper mantle discontinuities play an important role in understanding the nature of mantle processes. Data from several P NE seismic sounding profiles reveal reflections and refractions from upper mantle discontinuities at 410 and 660 kin depth. The amplitude and the sharpness of these velocity discontinuities contain important information to assess models of upper mantle phase changes and chemical layering. The absence of strong critical and precritical reflections from the 660 km discontinuity is characteristic for all the data in northern Eurasia. By studying the P wave reflections and refractions from the 660 km discontinuity, several velocity models were derived.To construct a generalized model, 18 shots observed on seven profiles in Russia were stacked to eliminate local effects. Synthetic seismograms were calculated and

Abstract. Tomographic inversion of Russian peaceful nuclear explosion (PNE) data collected along the 3500 km east-west striking profile Kraton has provided new information about the two-dimensional P-wave velocity structure of the upper mantle beneath the Siberian platform. The 8 ø discontinuity is clearly identified as the top of a zone in the 100-200 km depth range. This zone appears as a low-velocity zone in large parts of the profile and has zero velocity gradient along the profile. The 400 km discontinuity is imaged as an increase in velocity of at least 0.4 km/s at -380-420 km depth. BackgroundMajor upper mantle P-wave velocity discontinuities can be identified on a global scale. Global discontinuities that should be expected in continental mantle include the 8 ø discontinuity [Thybo and Perchurl, 1997] at about 100 km depth, the 400 km discontinuity [Jeffreys, 1936] , 1997]. In high-density long-range seismic sections the existence of the 8 ø discontinuity and the heterogeneous material below it are indicated by strongly scattered and delayed first arriving P-waves with a strong coda observed in the 700-1200 km offset range. The depth to the Lehmann Discontinuity depends on the thermal state of the mantle; it is deep in hot areas and shallow in cold areas. The other discontinuities may represent phase changes of the mantle rocks.Upper mantle velocity models are often based on long period body-wave and surface-wave earthquake data. Here we use seismic data with nuclear explosions as the controlled sources. The advantage is that the exact position in space and time of the source is known, and the dense average receiver spacing of 20 km along the 3500 km long profile Kraton provides a dense sampling of upper mantle phases. Other scientists have previously used other high-density PNE data sections for mapping 2D velocity variations in the lithosphere-asthenosphere First arrival travel time picksFour peaceful nuclear explosions (PNEs) were detonated along profile Kraton (Fig. 1) at intervals between 673 and 1168 km. In the 0 to -125 km offset range the first arriving P-waves are crustal waves (Fig. 2). From 125 to about 800 km offset the first arrivals are from the sub-Moho uppermost mantle. Strong scattering of the first arrivals in the 800 to -1300 km offset range is interpreted to be the effect of scatterers in the low-velocity interval below the 8 ø discontinuity. Strong reflections from this reflective low-velocity interval form a more than 5 s long coda of secondary arrivals in this offset range. The low-amplitude Lehmann refraction from below the low velocity interval is the first arrival between -1300 and 2000 km. In the 2100 to 2500 km offset range the apparent velocity of the first arrivals increases as typical for the 400 km discontinuity. From -1800 to -2500 km prominent reflections from the 400 km discontinuity are clear secondary arrivals. Beyond -2500 km offset the first arriving Pwaves originate from below the 660 km discontinuity.Observations similar to the ones mentioned above are made in ...