Q and its effect on the observation of upper mantle travel-time branches

Mathematics – Logic

Scientific paper

Rate now

  [ 0.00 ] – not rated yet Voters 0   Comments 0

Details

7

Scientific paper

There is broad agreement among various seismological studies that the upper mantle has two regions where high positive velocity gradients or transition zones exist. The presence of these zones implies that two major triplications should exist in the travel-time curve for distances less than 30°. Approximately 200 earthquakes from the New Guinea, New Britain, and Solomon Island regions recorded at the Warramunga Array were analyzed using adaptive processing methods in an attempt to identify the positions of the later arrival branches. From measurements made along the first 20 sec of the arrivals, a retrogade travel-time branch associated with the ``650-km'' discontinuity was clearly identified as extending from 21° to 26°, and some evidence was found near 16° for the lower portion of the triplication associated with the ``400-km'' discontinuity. A careful search revealed however that the upper portions of the replicated travel-time branches were missing. There were no observed values of dt/dΔ in the 12-13 sec/deg range for Δ greater than 20°. In this study it was found that if anelastic effects (Q) were not taken into consideration or if Q were kept constant, the models derived from observed travel-time data all predicted large amplitude arrivals where non existed. The difficulty with the first triplication was resolved by the introduction of a low Q region at depths of 85-315 km. This region may be associated with ``the low-velocity region'' but it is not necessary to decrease the P velocity to explain the observations. The difficulty with the second triplication was resolved by the introduction of a layer at a depth of 575-657 km which has no velocity gradient and a value of Q significantly less than that for the material just below the ``650-km'' discontinuity. This layer may well represent the return path for an upper mantle convection cell.

No associations

LandOfFree

Say what you really think

Search LandOfFree.com for scientists and scientific papers. Rate them and share your experience with other people.

Rating

Q and its effect on the observation of upper mantle travel-time branches does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Q and its effect on the observation of upper mantle travel-time branches, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Q and its effect on the observation of upper mantle travel-time branches will most certainly appreciate the feedback.

Rate now

     

Profile ID: LFWR-SCP-O-1797041

  Search
All data on this website is collected from public sources. Our data reflects the most accurate information available at the time of publication.