Postcritical sspmp, the seismic phase used in vdss, originates when upcoming teleseismic s waves convert to downgoing p waves at the free surface the virtual source, and then undergo postcritical reflection at or within the cmb and finally reach the receiver fig. Jones ion geophysical summary conventional seismic data processing, whether it be prestack data conditioning or migration, is designed with the theory of pwave reflected energy inmind, for travel paths involving only a single reflection. One reflection and one refraction x critical s i c i v 1 v 2 v 1 direct refr headwave. Jones abstract conventional seismic data processing, whether it be prestack data conditioning or migration, is designed with the theory of pwave reflected energy inmind, for travel paths involving only a single reflection. Analysis of pstopp amplitude ratios for seismic reflector characterisation. The propagation depends on many parameters, such as structure of material, stressstrain state and the frequency of waves 9, 10. Sspmp, the seismic phase used in vdss, originates when upcoming teleseismic s waves convert to downgoing p waves at the free surface the virtual source, which then undergo postcritical reflection at or within the crustmantle boundary cmb and finally reach the receiver fig. The land dynsmite wavelet is unmeasurable, but can be extracted from the plane wave reflection response at post critical incidence. Geothermal fields in the basin and range province are commonly found in highly faulted and fractured subsurface zones that provide the necessary permeability for vertical fluid flow.
Related subduction systems seismic structure, intraslab earthquakes and processes, and earthquake hazards edited by stephen kirby1, kelin wang2, and susan dunlop3 released simultaneously as u. Basically, seismic waves are subjected to scattering, reflection etc. The travel time inversion of wideangle seismic data is a technique commonly used in the deep seismic sounding. To arrive at the reflection response the data has to be deconvolved for the source wavelet and scaled to convert the recorded data in volts to the field variable ms2. Regional crustal structure derived from the cdrom 99. Mit opencourseware earth, atmospheric, and planetary. The nearnormalincidence polarity measurements support the suggestion that both the flannan and wreflectors represent an eclogitic slab, presumably a relict oceanic.
Snells law in spherical media ray equation radius of curvature. Phase shifts and pulse distortion layer over half space courtesy of lori eich. Virtual deep seismic sounding vdss has recently emerged as a novel method to image the moho and potentially other lithospheric boundaries. Csm department of geophysics thesis listings last name. Statistical approaches to interpretation of seismic. Critical and postcritical reflection courtesy of clare williams. The uncertainty of the reflection seismic imaging from analysis of wideangle postcritical reflections. Reprocessing of high resolution seismic reflection data from vihanti, finland.
Sharma p158 186 applied geophysics refraction i precritical incidence snells law. The moho reflection pmp is present on all record sections. Seismic reflection data from near to postcritical angles provide the potential of both velocity and density inversion. To illustrate the deeper structure, we also present a long. Here, motivated by observations from the ordos plateau in north china, we use. Seismic detection of folded, subducted lithosphere at the. The seismic response to strong vertical velocity change i.
Waveform inversion of deep seismic reflection data. The seismic response to strong vertical velocity change ian f. Geological survey openfile report 02328 and geological survey of canada open file 4350 version 1. The seismic response to strong vertical velocity change. Neglecting this phaseshift correction in wideangle seismic pro. Phase shift approximation for the postcritical seismic wave incidence aki and richards 1980. Complex data are formed from real data by removing the negative frequency portion of the fourier transform and doubling the positive frequency portion.
Bedrock imaging using postcritical shallow seismic. Refraction seismic method intercept times and apparent velocities. There are many methods to calculate residual statics solutions, such as reflection stackpower maximization method ronen and claerbout, 1985. Residual statics due to nearsurface velocity variations may not be able to be resolved through the nearsurface model imaging, but critical for seismic data processing. P and swave reflection amplitudes usually vary with incidence angles. Converting the seismic section from time to depth b.
Nearoffset reflection and multifold wideaperture data are simultaneously recorded along two profiles in a small basin crossed by an active fault in southern italy. In reflection seismologywe tend to use artificially induced vibrations created by a variety of seismic sources. Field observations confirmed by synthetic analysis recognize the dominant amplitudes of wide. Nsffunded marine seismic research june 2010 appendix h. Jones, ion gx technology summary conventional seismic data processing, whether it be prestack data conditioning or migration, is designed with the theory of pwave reflected energy inmind, for travel paths involving only a single reflection. Combining this greens function with the multichannel prediction operator, we. Use of postcritical seismic reflection amplitudes, for exploration purposes, including depth estimation 2 copies alfaraj mohammed phd 1993 t4344 transformation to zero offset formodeconverted waves. Pwave reflection and transmission amplitudes are determined by the contrast in acoustic impedance z. Seismic resolution is the ability to distinguish separate features. Inversion of a land seismic data set after extraction of. Elastic parameters derived from seismic reflection data provide information on the lithological.
The behaviour of sspmp, the postcritical reflection phase at the moho that is utilized in vdss, is rich with complexities not yet widely considered. This unexpected phase can be explained by postcritical reflection of p waves at the deep seismic zone after strong focusing by the. What is the maximum geophone offset which you would use to avoid postcritical phase distortion. Conventional processing stacking and migration provides very. As discussed in earlier lectures, the equation of motion for a homogenous elastic medium has solutions. The lowermost crustal phase plp often has high amplitudes as well, but its amplitude is exceeded by the midcrustal reflector pcp on some shot records figures 6 9. The lithologic log information corroborated the feasibility of imaging subsurface structure from postcritical reflection data by conventional processing, provided additional velocitydepth. Bedrock imaging using postcritical shallow seismic reflection data statistical approaches to composite endpoints. Reflection traveltimes single layer t x 4h2 x2 v 2 h v 2 x v 2 t0 2 x v 2 tx is called the hyperbolic normal reflection moveout nmo x critical s i c i v x t d i r e c t h e a d re f l e c t e d t 0 h precritical region postcritical region. Nonetheless, the inversion suggests a positive polarity for the wreflector, in agreement with observations of postcritical reflections seen on wideangle seismic data. Beyond 50 degrees, the reflection coefficient increases rapidly and approaches a value of 1 total reflection near 90 degrees. Deep seismic zone as an upper mantle reflector of body. Find materials for this course in the pages linked along the left. We propose an application of this technique to a smaller scale of a sedimentary layer, where the characteristics of seismic observations changes significantly.
This study utilizes a 2d seismic reflection line to explore the geophysical signature of the san emidio geothermal fields production zone, located in nw nevada. A refraction seismic survey is conducted in a region with a planar, dipping layer beneath a flat overburden layer. Note that the postcritical reflection behavior of the shaletosalt boundary includes a 180 degree phase change and very high reflection coefficient. Request pdf seismic velocity estimation from postcritical wideangle reflections in layered structures the travel time inversion of wideangle seismic. Adjusting the reflection time based on the hyperbolic travel time c. Seismic wave packets generated by blasting in underground mines propagate in rock mass in all directions. Development and application of avo methods and seismic. Postcritical sspmp and its applications to virtual deep. Phase shift approximation for the postcritical seismic wave. A method for processing seismic data includes obtaining a velocity model, determining a critical angle for an interface represented in the velocity model based on a ratio between velocity of the seismic wave on first. It is known that plane wave solutions are inapplicable near the critical angle. The elastic reflection modelling was decisive to perform the postcritical seismic reflection survey, and to check the reliability of our interpretation. Reflection seismic method university of saskatchewan.