We show that the work of O'Doherty & Anstey can be used to deduce apparent attenuation acoustic waves in randomly layered media:

This old standard text has undergone its first face‐lift since 1963 third edition. Its length been increased from 381 pages to 499, size 14.5×22.0 cm 15.5×23.5 cm, the number of equations 433 859, figures 43 96, date most recent reference 1962 1985, and price $9.50 $69.50. Problems have added end each chapter, an appendix earth models (e.g., Preliminary Earth Reference Model) book. As Bolt states in preface, “About sixty percent this edition is new material.”

We report the results of some numerical experiments that bring out lowpass characteristics a purely elastic medium with heterogeneous velocity structure. Although typical fluctuation is spatially confined within less than wavelength, waves propagating over sufficiently long path suffer major cumulative effects. summarize removal high frequencies during transmission by frequency-independent apparent Q, and show attenuation intrinsic friction scattering are approximately additive. propose...

The 170 km South Iceland Seismic Tomography (SIST) profile extends from the west and across Mid‐Atlantic Ridge spreading center in Western Volcanic Zone continues obliquely through transform zone (the Zone) to western edge of Eastern Zone. A total 11 shot points 210 receiver were used, allowing precise travel times be determined for 1050 crustal P wave rays 180 wide‐angle reflections. large amplitudes reflections an apparent refractor velocity 7.7 km/s are interpreted a relatively sharp Moho...

A simple mathematical inverse method is used to correlate two time series D ( x ) and R t ), where these signals are related each other by the mapping function ). The describes stretching squeezing of one signal with respect other. assumes that known, while not. parameterized in terms a sum functions unknown coefficients i ;. These estimated from assumption best those which maximize coherence between [ )]. maximization performed iteratively, beginning some initial estimate . standard error...

Observations of shear wave splitting in the northeastern U.S. Appalachians and foredeep Urals vary significantly with back azimuth incidence angle incoming phase. These variations suggest two or more layers within upper mantle different anisotropic properties. Synthetic seismograms for simple multilayered structures show that parameters tend to substantially direction approach. Relying on a subset back‐azimuth may strongly bias model inferred, especially if observations are averaged. On...

Results from the Färoe‐Iceland Ridge Experiment (FIRE) constrain crustal thickness as 19 km under Northern Volcanic Zone of Iceland and 35 older Tertiary areas northeastern Iceland. The Moho is defined by strong P wave S reflections. Synthetic seismogram modeling reflection indicates mantle velocities at least 8.0 km/s beneath 7.9 neovolcanic zone. Crustal diving rays resolve structure upper lower crust. Surface are 1.1–4.0 in Quaternary rocks rather higher, 4.4–4.7 km/s, basalts that...

The seismic velocity structure of the Krafla central volcano is characterized by large variations in compressional velocity. A 40 km wide high‐velocity dome extends from lower crust (11–14 depth) beneath narrowing upward. magma chamber sits at its top near 3 depth. It defined both 0.2–0.3 s wave delays and shear shadowing to be 2–3 N‐S, 8–10 E‐W, 0.7–1.8 thick. near‐surface (uppermost 2.5 km) caldera approximately flat‐lying, with only minor lateral heterogeneities. has low attenuation...

Teleseismic P n waves are modeled as a sum of whispering galley waves, which propagate in waveguide composed simple high velocity mantle lid underlain by low zone. This model is able to account for those wave propagation properties that not dominated scattering, i.e., their apparent and lack long period energy. data constrain the gradient upper 100 km be low; dv p /dz<0.001 s −1 . The gallery rays shown have significant amplitude (when compared direct wave) spectra rapidly fall off at...

The data collected in a cross‐borehole tomography problem is inherently incomplete, since the boreholes do not completely surround media under study. ability of experiment to resolve structure therefore limited by poor experimental geometry. We use method Backus and Gilbert investigate this technique variations acoustic velocity attenuation between two boreholes. Both integrals that appear Backus‐Gilbert formulation can be performed analytically, thus expediting calculations. resolving...

The cross‐correlation of multicomponent ambient seismic noise can reveal both the velocity and polarization surface waves propagating between pairs stations. We explore this property to develop a novel method for determining horizontal orientation ocean bottom seismometers (OBS) by analyzing Rayleigh retrieved from cross‐correlation. demonstrate that sensor orientations be estimated through maximizing correlation radial‐vertical component phase‐shifted vertical‐vertical empirical Green's...

Abstract The Northern Appalachian Anomaly (NAA) is an intense, laterally localized (400 km diameter) low‐velocity anomaly centered in the asthenosphere beneath southern New England. Its maximum shear velocity contrast, at 200 depth, about 10%, and its compressional‐to‐shear perturbation ratio unity, values compatible with it being a modern thermal anomaly. Although close to track of Great Meteor hot spot, not elongated parallel does crosscut cratonic margin. In contrast previous...

We present a new method for determining anisotropic earth models using observations of split shear waves (such as SKS). The consists first constructing two time-series, x(t) and y(t), that contain information concerning both the observed seismograms hypothetical model, then varying model so to minimize misfit, e(t) =x(t) −y(t). time-series are defined by rules, =hpre (m, t)*Vobs(t) y(t) =vpre(m, t)*Hobs(t), where Vobs(t) Hobs(t) radial-horizontal tangential-horizontal component seismograms,...

Information on the time intervals between large earthquakes is now available for several fault segments along plate boundaries in Japan, Alaska, California, Cascadia, and Turkey. When dates a sequence are known historically, as much of Nankai trough, they provide information natural (intrinsic) variability rupture process. Most sets repeat times, however, dominated by paleoseismic determinations older earthquakes, which contain measurement uncertainties addition to intrinsic variability. A...

Results of a 2-D, seismic undershooting experiment on the Katla central volcano in south Iceland are reported. Large localized traveltime anomalies (0.4s) observed an array within caldera. The traveltimes forward modelled using wavefront tracker developed Appendix A. Thus, non-linear effects encountered tomography avoided as well common problems with ray tracing presence strong lateral heterogeneity. extreme variation compressional velocity is required to extend over significant volume order...

Abstract Tectonic forces alone cannot drive rifting in old and thick continental lithosphere. Geodynamic models suggest that thermal weakening is critical for lithospheric extension, yet many active rifts lack volcanism, seeming to preclude this process. We focus on one such rift, the Tanganyika-Rukwa segment of East African Rift System, where we analyze local seismicity shear wave anisotropy couple results with numerical modeling. The strongest splitting measurements are from earthquakes...

Abstract Except for its very onset, the P wave of earthquakes and chemical explosions observed at two narrow-aperture arrays on hard-rock sites in Adirondack Mountains have a nearly random polarization. The amount energy vertical, radial, transverse components is about equal over frequency range 5 to 30 Hz, entire seismogram. spatial coherence seismograms approximately exp(−cfΔx), where c 0.4 0.7 km−1Hz−1, f Δx distance between array elements. Vertical, were quite coherent aperture array,...

Abstract The geological record of SE Canada spans more than 2.5 Ga, making it a natural laboratory for the study crustal formation and evolution over time. We estimate thickness, Poisson's ratio, proxy bulk composition, shear velocity ( V s ) structure from receiver functions at network seismograph stations recently deployed across Archean Superior Craton, Proterozoic Grenville, Phanerozoic Appalachian provinces. seismic properties reveal correlation with tectonic provinces different ages:...

Very little seismic attenuation occurs in the mid to lower crust of south-west Iceland. The lowest path-averaged quality factor for a wave turning (12–20 km) is QP= 110 P waves and QS= 250 S waves, with most data having higher values, typically 200–300 400–600. Attenuation estimates based on 1-D, layered inversion give correspondingly high QP > 800 800–2000. These Q values are inconsistent thermal models that predict broad (100 km wide) region above-solidus temperatures centred volcanic...