Download or read book Seismicity and Structure of the Orozco Transform Fault from Ocean Bottom Seismic Observations written by and published by . This book was released on 1982 with total page 370 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Seismicity and Structure of the Orozco Transform Fault from Ocean Bottom Seismic Observation Anne Martine Tr hu written by Anne Martine Tréhu and published by . This book was released on 1982* with total page 588 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Seismicity and Structure of the Orozco Transform Fault from Ocean Bottom Seismic Observations written by Anne Martine Tréhu and published by . This book was released on 1982 with total page 371 pages. Available in PDF, EPUB and Kindle. Book excerpt: Seismic waves generated by sources ranging from 2.7 kg shots of TNT to magnitude 5 earthquakes were studied in order to determine the seismic activity and crystal structure of the Orozco transform fault. Most of the data were collected by a network of 29 ocean bottom seismometers (OBS) and hydrophones (OBH) which were deployed as part of a project ROSE (Rivera Ocean Seismic Experiment). Additional information was provided by magnetic anomaly and bathymetric data collected during and prior to ROSE and by teleseismic earthquakes recorded by the WWSSN (Worldwide Seismic Station Network). (Author).

Download or read book Seismicity and Structure of the Orozco Transform Fault written by Anne Martine Tréhu and published by . This book was released on 1982 with total page 740 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Seismic Attenuation Structure of the East Pacific Rise written by William Sam Douglas Wilcock and published by . This book was released on 1992 with total page 356 pages. Available in PDF, EPUB and Kindle. Book excerpt: Studies of seismic propagation through oceanic crust have contributed enormously to our understanding of the generation and evolution of oceanic crust However, such work has largely been confined to the seismic velocity structure. In this thesis we present results from a study of seismic attenuation using a data set collected for three-dimensional tomographic imaging of a fast-spreading ridge. The experiment location at 9°30'N on the East Pacific Rise is the site of a strong mid-crustal seismic reflector which has been inferred to be the roof of a small axial magma chamber at about 1.6 km depth. A spectral method is used to estimate t*, a measure of the integrated attenuation along a wave path. Such a method asswnes that the dominant frequency-dependent component of propagation is intrinsic attenuation. A logarithmic parameterization is then used to invert t* measurements for Q-1 structure asswning that the velocity structure is given from earlier studies. To evaluate the method of Q tomography a full-waveform finitedifference technique which does not include attenuation is used to calculate solutions for seismic propagation through a two-dimensional velocity model. The results show a complex pattern of seismic propagation in the vicinity of the axial magma chamber. The first arrival always passes above the magma chamber. However, for paths of significant length that cross the rise axis the amplitude of this arrival is very small, and the first phase with significant amplitude is a diffraction below the magma chamber. High-amplitude Moho turning and PP arrivals may also be important secondary arrivals. Synthetic inversions show the importance of selecting time windows for power spectral estimation which are dominated by a single phase and of using wave paths which closely corresponds to that of the selected phase. A comparison of the finite difference solutions and the predictions of the a twodimensional, exact ray-tracing algorithm with record sections obtained during the tomography experiment significantly improves our understanding of seismic propagation across the East Pacific Rise. The results enable an objective choice of the position and length of the time window fort* estimation. Moreover, additional constraints are incorporated into an approximate three-dimensional ray-tracing algorithm used in the inversion so that the wave paths more closely correspond to those of the desired phase. The full data set to be inverted comprises about 3500 t* estimates and includes crustal paths which do not cross the rise axis, diffractions above and below the axial magma chamber, and Moho-turning phases. Wave paths for the Moho-turning phases cross the rise axis at a wide range of lower crustal depths. The Q-1 models resulting from two-dimensional and three-dimensional tomographic inversions show that the attenuation of seismic waves on the East Pacific Rise is dominated by two regions of low Q; one in the upper 1 km of crust, and one at depths greater than about 2 km below the rise axis. While the data do not resolve the details of vertical variations in near-surface Q-1, the results show a substantial variation in shallow attenuation within 0.05 My of the rise axis. On-axis, Q values averaged over the upper 1 km are about 100, while off-axis the average value rapidly decreases to about 30. Measurements of the seismic velocity suggest that the thickness of the surficial highporosity extrusive layer increases substantially off-axis. If such thickening is entirely responsible for the observed change in near-surface attenuation then Q within the extrusive layer must be much less than 20. Alternatively, in situ changes in porosity may also contribute to the observed increase in attenuation. Since significant tectonic activity is apparently restricted to locations well off-axis we suggest that such variations in porosity may result from hydrothermal activity. Regions of hydrothermal downwelling located off-axis will be subject to cooling and thermally-induced cracking while upwelling regions on-axis may be accompanied by rapid infilling of existing pores by hydrothermal deposits. Estimates of t* for all phases propagating below the magma chamber are markedly higher than those for other phases, resulting in Q-1 models which include a region of low Q extending from 2 to 7 km depth below the rise axis. The lowest Q values resolved are about 25-30 both immediately below the magma chamber and within the lower crust. While there is some evidence for a small decrease in attenuation with depth in the lower crust, axial Q values at depths ranging from less than 2.5 to 6 km are relatively constant, always lying below 50. Laboratory measurements at seismic frequencies suggest that Q values of 25-50 require only very small fractions of partial melt. The attenuation observations thus place constraints on the dimensions of the axial magma chamber and strongly suggest that the thickness of the region containing more than a few percent of partial melt is no more than 1 km.

Download or read book Bibliography of Technical Reports written by Woods Hole Oceanographic Institution and published by . This book was released on 1982 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Earthquake Behavior and Structure of Oceanic Transform Faults written by Emily Carlson Roland and published by . This book was released on 2012 with total page 149 pages. Available in PDF, EPUB and Kindle. Book excerpt: Oceanic transform faults that accommodate strain at mid-ocean ridge offsets represent a unique environment for studying fault mechanics. Here, I use seismic observations and models to explore how fault structure affects mechanisms of slip at oceanic transforms. Using teleseismic data, I find that seismic swarms on East Pacific Rise (EPR) transforms exhibit characteristics consistent with the rupture propagation velocity of shallow aseismic creep transients. I also develop new thermal models for the ridge-transform fault environment to estimate the spatial distribution of earthquakes at transforms. Assuming a temperature-dependent rheology, thermal models indicated that a significant amount of slip within the predicted temperature-dependent seismogenic area occurs without producing large-magnitude earthquakes. Using a set of local seismic observations, I consider how along-fault variation in the mechanical behavior may be linked to material properties and fault structure. I use wide-angle refraction data from the Gofar and Quebrada faults on the equatorial EPR to determine the seismic velocity structure, and image wide low-velocity zones at both faults. Evidence for fractured fault zone rocks throughout the crust suggests that unique friction characteristics may influence earthquake behavior. Together, earthquake observations and fault structure provide new information about the controls on fault slip at oceanic transform faults.

Download or read book Curricula in the Atmospheric and Oceanographic Sciences written by American Meteorological Society and published by . This book was released on 1984 with total page 388 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book U S Geological Survey Circular written by and published by . This book was released on 1984 with total page 614 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Technical Abstract Bulletin written by and published by . This book was released on 1982 with total page 250 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Highlights in Marine Research written by and published by . This book was released on 1984 with total page 186 pages. Available in PDF, EPUB and Kindle. Book excerpt: The reports and abstracts in this volume illustrates the breadth and depth of U.S. Geological Survey (USGS) research in marine geology.

Download or read book Pollution Abstracts written by and published by . This book was released on 1983 with total page 954 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The United States Geological Survey in Alaska written by and published by . This book was released on 1984 with total page 722 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book American Doctoral Dissertations written by and published by . This book was released on 1981 with total page 552 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Safety Science Abstracts Journal written by and published by . This book was released on 1983 with total page 1072 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Geophysical Journal of the Royal Astronomical Society written by and published by . This book was released on 1985 with total page 828 pages. Available in PDF, EPUB and Kindle. Book excerpt: Vols. 11 and 13 includes the Proceedings of the 2nd, 3rd, International Symposium on Geophysical Theory and Computers, Rehovoth, Israel, etc., 1965-66.

Download or read book Government Reports Annual Index written by and published by . This book was released on 1982 with total page 1010 pages. Available in PDF, EPUB and Kindle. Book excerpt: Sections 1-2. Keyword Index.--Section 3. Personal author index.--Section 4. Corporate author index.-- Section 5. Contract/grant number index, NTIS order/report number index 1-E.--Section 6. NTIS order/report number index F-Z.