This map shows the predicted (theoretical) travel times, in minutes, of the compressional (P) wave from the earthquake location to points around the globe. The travel times are computed using the spherically-symmetric IASP91 reference earth velocity model. The heavy black lines shown are the approximate distances to the P-wave shadow zone (103 to 140 degrees).

The shadow zone is the area of the earth from angular distances of 104 to 140 degrees from a given earthquake that does not receive any direct P waves. The shadow zone results from S waves being stopped entirely by the liquid core and P waves being bent (refracted) by the liquid core.
Through measuring how P and S waves travel through the earth and out the other side, a seismic wave shadow zone was discovered in about 1910. From the lack of S waves and a great slowing of the P wave velocity (by about 40%) it was deduced that the outer core is made of liquid. The shadow zone also defined the diameter of the core.

Attenuation tomography revealed lateral complexity for northern Italy that comprises the Alps–Apennines junction zone and the foredeep basin (Po Plain) of both chains. The results consistently show the same trend for different frequency bands and for both coda and direct waves, though lateral coda attenuation is smoother, especially for high and low frequencies.
A low attenuation area is observed in the southern part of the western Alps characterized by the presence of crystalline massifs. To the north of this zone, in the western Alps, a large low Q anomaly is observed in correspondence with the Ivrea body. The large range of frequency in which the anomaly is observed indicates a variable scale length of the heterogeneity.
The results also show high Q under the Po Plain, the largest alluvial basin of northern Italy. This region has a complex geological and structural setting because the thrust fronts of the northern Apennine are buried by variable thickness, quaternary alluvium, which might cause the anomalous propagation.

The 2D inversion results for direct waves for all analyzed frequency bands. The value of (Q) at the bottom of each image is the average quality factor for the resolved area (the colored portion of each map) for each frequency. The color scale indicates the variation in percentage with respect to (Q). White triangles represent the stations while black circles are the events used for each inversion.

Q tomography results for coda waves at all frequency bands. Each image shows the variation of Q in percentage with respect to the average value reported at the bottom of each image (〈Q〉). The colored portion of each map delineated the region where we have good resolution. White triangles represent the stations while black circles are the events used for each inversion.

Some results of the study the upper mantle P wave velocity structure below the Euro-Mediterranean area, down to 1000 km depth, by seismic travel time tomography.

Cross sections through some of the main features of the velocity model. The top map illustrates the section location. Each cross section has the same length (approximately 20o along a great circle) and its vertical extent reaches the bottom of the model. Ticks along the line segment indicate the distance from the extremities by 5o intervals. Below the map, one panel is plotted: the panel for the model. Ticks at 5o intervals along the upper axis of the panel correspond to the locations along the section line segment plotted on the map. The 410 and 660 km discontinuities are indicated as a thin and thick lines, respectively.

 A-a - Low velocity heterogeneity beneath the Massif Central (topmost 250 km). The synthetic test shows that the central portion of the section is well resolved, but some vertical leaking occurs and the narrow, conduit-like structure is probably not a robust feature.
 B-b - Section running approximately along the European Geotraverse. A fast feature deepens from the surface below the central Alps, its strongest portion reaching about 200 km depth. From ray sampling and the impulse recovery test, we expect a good resolution in the central portion of the section. Notice also the accumulation of fast material between 400 and 800 km.
 C-c - Shallow fast anomaly below the northern Adriatic Sea possibly connected with the fast structure, below the northern Apennines. On the Tyrrhenian side, a wedge-shaped slow anomaly just above the slab merges with the lower amplitude western Mediterranean slow anomaly down to 400 km depth.
 D-d - Strong slow anomaly beneath the central Apennines (0–250 km depth). To the east, the fast Adriatic lithosphere deepens below the Dinarides.
 E-e - High velocity anomaly on the Ionian side of the Calabrian Arc connected to the fast structure steeply dipping below the arc into the mantle and bending horizontally in the transition zone. The synthetic test indicates that horizontal smearing may result in artifacts along this section at midmantle depths.
  F-f - Fast material can be followed from the surface through the upper mantle, across the 670 km discontinuity and down to the bottom of the model in the Hellenic Trench. A large amplitude, well sampled, low anomaly wedge is found in correspondence of the Aegean Basin. Correlation between density of rays and shape of input anomalies indicates that smearing of these small anomalies likely occurs in the deeper part.