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— Starting with fundamental-mode Rayleigh-wave attenuation coefficient values (γ R ) predicted by previously determined frequency-independent models of shear-wave Q (Q μ ), we have obtained frequency-dependent Q μ models that explain measured values of γ R as well as of Lg coda Q and its frequency dependence at 1 Hz (Q o and η, respectively) for China and some adjacent regions. The process combines trial-and-error selection of a model for the depth distribution of the frequency dependence parameter (ζ) for Q μ with a formal inversion for the depth distribution of Q μ at 1 Hz. Fifteen of the derived models have depth distributions of ζ that are constant, or nearly constant, between the surface and a depth of 30 km. ζ distributions that vary with depth in the upper 30 km are necessary to explain the remaining seven models. ζ values for the depth-independent models vary between 0.4 and 0.7 everywhere except in the western portion of the Tibetan Plateau where they range between about 0.1 and 0.3 for three paths. These low ζ values lie in a region where QLg and crustal Q μ are very low and suggest that they should also be low for high-frequency propagation. The models in which ζ varies with depth all show a decrease in that value ranging between 0.55 and 0.8 in the upper 15 km of the crust and (with two exceptions where ζ=0.0) between 0.3 and 0.55 in the depth range 15–30 km. The distribution of ζ values between 0.6 and 0.8 (the higher part of the range) in the upper crust indicates that high-frequency waves will propagate most efficiently, relative to low-frequency waves, in a band that includes, and strikes north-northeastward from the path between event 212/97 and KMI to the path between event 180/95 and station HIA in the north.

Nine broadband seismograph stations in South America have provided 389 recordings of Lg coda with paths that cover most of the continent. Lg coda Q (Q 0) and frequency dependence (η) values at 1 Hz, obtained from these records, were inverted using back-projection tomography to obtain regionalized maps of Q 0 and η. The entire western margin of the continent (the active Andean mountain belt) is typified by low Q 0 (250–450), whereas broad regions of high Q 0 (700–1100) span the central Brazilian shield and contiguous regions to the north and south. Intermediate Q 0 (450–700) characterizes the northern Patagonia platform and most of the Atlantic shield. Reduced Q 0 in the Atlantic shield may be related to tectonic or igneous activity that occurred during the breakup of Gondwanaland during the Jurassic period. This Q distribution is generally consistent with earlier studies where go was found to be directly proportional to the time that has elapsed since the most recent episode of major tectonic or orogenic activity in any region. Reduced Q 0 in the Patagonian platform may, however, be due to young sediments there.

In the journal version of the special issue ‘‘Q of the Earth: Global, Regional, and Laboratory Studies’’ edited by Barbara Romanowicz and Brian J. Mitchell, but not in its reprint as a book, page 594 of the above mentioned article by mistake presents two figures, termed Figs. 3 and 4, for the situation in Australia together with two legends for Figs. 5 and 6, which refer to the situation in South America. The correct figures for South America are as follows

The first nuclear bomb was detonated in 1945, thus ushering in the nuclear age. A few political leaders quickly saw a need to limit nuclear weapons through international cooperation and the first proposals to do so were made later that same year. The issue of nuclear testing, however, was not formally addressed until 1958 when the United States, the United Kingdom, and the Soviet Union, initiated talks intended to establish a total ban on that testing (a Comprehensive Test-Ban Treaty or CTBT). Those talks ended unsuccessfully, ostensibly because the participants could not agree on the issue of on-site verification.

Few aspects of seismic wave propagation have aroused as much disagreement among seismologists as that of seismic wave attenuation (or its inverse Q). Areas of disagreement include (1) the physical causes of the attenuation, (2) the relative contributions of scattering and intrinsic absorption at various frequencies during propagation, and (3) the nature of the frequency dependence of Q. Seismologists, in their publications, have largely avoided addressing these disagreements by ignoring all papers promoting a perspective differing from their own. This forum seeks to remedy that situation for issue (3), the nature of Q frequency dependence. Igor Morozov has recently published a number of papers in which he concludes that there is no compelling reason to think that Q varies at all with frequency. This revolutionary result, if correct, negates almost all of the work on Q frequency dependence that seismologists have reported going back to at least the mid-1970s. In the spirit of having an open and full discussion of the nature of Q frequency dependence (or the lack thereof) I have convened a forum to discuss Dr Morozov’s recently proposed methodology. He has agreed to defend his method and ensuing results and Dr Jiakang Xie has agreed to argue the case against the new approach and to defend the traditional way of looking at Q frequency dependence. If you would like to participate in this forum I invite you to send your comments to me (bmitche8@slu.edu) in an email attachment. Comments will appear in a special section on Forum Responses in the November issue of PAGEOPH. Please restrict all comments to one manuscript page or, at most, two.

—Observed velocities and attenuation of fundamental-mode Rayleigh waves in the period range 7–82 sec were inverted for shear-wave velocity and shear-wave Q structure in the Middle East using a two-station method. Additional information on Q structure variation within each region was obtained by studying amplitude spectra of fundamental-mode and higher-mode Rayleigh waves. We obtained models for the Turkish and Iranian Plateaus (Region 1), areas surrounding and including the Black and Caspian Seas (Region 2), and the Arabian Peninsula (Region 3). The effect of continent-ocean boundaries and mixed paths in Region 2 may lead to unrealistic features in the models obtained there. At lower crustal and upper-mantle depths, shear velocities are similar in all three regions. Shear velocities vary significantly in the uppermost 10 km of the crust, being 3.21, 2.85, and 3.39 km/s for Regions 1, 2, and 3, respectively. Q models obtained from an inversion of interstation attenuation data show that crustal shear-wave Q is highest in Region 3 and lowest in Region 1. Q’s for the upper 10 km of the crust are 63, 71, and 201 for Regions 1, 2, and 3, respectively. Crustal Q’s at 30 km depth for the three regions are about 51, 71, and 134. The lower crustal Q values contrast sharply with results from stable continental regions where shear-wave Q may reach one thousand or more. These low values may indicate that fluids reside in faults, cracks, and permeable rock at lower crustal, as well as upper crustal depths due to convergence and intense deformation at all depths in the Middle Eastern crust.

Regional seismograms were collected to image the lateral variations of Lg coda Q at 1 Hz (Q 0) and its frequency dependence (η) in the Middle East using a back-projection method. The data include 124 vertical-component traces recorded at 10 stations during the period 1986–1996. The resulting images reveal lateral variations in both Q 0 and η. In the Turkish and Iranian Plateaus, a highly deformed and tectonically active region, Q 0 ranges between about 150 and 300, with the lowest values occurring in western Anatolia where extremely high heat flow has been measured. The low Q 0 values found in this region agree with those found in other tectonically active regions of the world. Throughout most of the Arabian Peninsula, a relatively stable region, Q 0 varies between 350 and 450, being highest in the shield area and lowest in the eastern basins. All values are considerably lower than those found in most other stable regions. Low Q values throughout the Middle East may be caused by interstitial fluids that have migrated to the crust from the upper mantle, where they were probably generated by hydrothermal reactions at elevated temperatures known to occur there. Low Q 0 values (about 250) are also found in the Oman folded zone, a region with thick sedimentary deposits, η varies inversely with Q 0 throughout most of the Middle East, with lower values (0.4–0.5) in the Arabian Peninsula and higher values (0.6–0.8) in Iran and Turkey. Q 0 and η are both low in the Oman folded zone and western Anatolia.