On time-distance curves for Pn waves in the Friuli earthquake of 6 May 1976

Abstract

Results obtained in the study of the arrival times of the Pn phase for the Friuli earthquake of 6 May 1976 (H = 20h00™15s,5; Normal 0 14 false false false MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:Tabella normale; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:; mso-padding-alt:0pt 5.4pt 0pt 5.4pt; mso-para-margin:0pt; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:Times New Roman; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} φ = 46° 16'30 N; Normal 0 14 false false false MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:Tabella normale; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:; mso-padding-alt:0pt 5.4pt 0pt 5.4pt; mso-para-margin:0pt; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:Times New Roman; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} λ = 13° 06' 00 E; M = 6.3) with respect to the epicentral distance are reported. Particular emphasis is given to the fact that the travel-time curves relative to the Pn waves and the corresponding equations are only valid for selected alignment. By plotting the time-distance curves it was possible to derive the depth of the lower surface of the upper mantle for different zones; the results thus obtained exibit significant differences.