scholarly journals Assessing uncertainties in high-resolution, multifrequency receiver-function inversion: A comparison with borehole data

Geophysics ◽  
2018 ◽  
Vol 83 (3) ◽  
pp. KS11-KS22 ◽  
Author(s):  
Nicola Piana Agostinetti ◽  
Alberto Malinverno
Keyword(s):  
Wave Velocity ◽  
Receiver Function ◽  
Joint Inversion ◽  
Seismic Station ◽  
Velocity Ratio ◽  
Earth Model ◽  
Elastic Model ◽  
S Wave ◽  
Borehole Data ◽  
Sonic Log

We use teleseismic P-to-S converted waves from a permanent station to estimate the uncertainties in a 1D elastic model of the shallow crust (0–7 km depth) obtained from the inversion of receiver function (RF) data. Our earth model consists of layers with a constant S-wave velocity [Formula: see text] and P- to S-wave velocity ratio ([Formula: see text]). We apply a Bayesian formulation and transdimensional Monte Carlo sampling to compute the posterior uncertainties of the earth model. The model uncertainties rely on a realistic representation of the data uncertainties, and we estimate directly from the stacking of the teleseismic data, a full-error covariance matrix. To explore the effect of the number of teleseismic events and the RF frequency content, we compare the results of inverting a single RF computed for a cut-off filter frequency of 4 Hz with the joint inversion of four RFs computed from independent ensembles in a larger pool of events for cut-off frequencies of 0.5, 1, 2, and 4 Hz. The inversion results are compared with the lithostratigraphy and sonic-log measurements from a 7 km deep borehole drilled near the seismic station. The inversion of a single RF results in larger uncertainties in the recovered [Formula: see text] profile and in the depth to seismic discontinuities compared with the multifrequency inversion. Moreover, the multifrequency inversion predicts more accurately the depth to a velocity inversion at approximately 6 km below the surface and matches more closely the borehole sonic-log data. Our results indicate that RF data can be used to map shallow (3–5 km depth) crustal interfaces with uncertainties in the order of 300–500 m, whereas uncertainties are consistently smaller (<300 m) for interfaces in the top kilometer.

scholarly journals Receiver function seismology

2019 ◽  
pp. 16-27
Author(s):  
L. P. Vinnik
Keyword(s):  
Transition Zone ◽  
Wave Velocity ◽  
Receiver Function ◽  
Velocity Ratio ◽  
Receiver Functions ◽  
Tien Shan ◽  
Function Technique ◽  
S Wave ◽  
Crust And Upper Mantle ◽  
Mantle Transition Zone

The application results of the receiver function technique are briefly outlined. The topography of the main seismic boundaries in the mantle transition zone is evaluated with resolution of about 3 km in depth and about 200 km laterally. The maximal amplitudes of depth variations of the main boundaries reach tens of kilometers. The mantle transition zone thinning in the hot spots and the respective increase in temperature by ~100 °C is established. In several regions, two low-velocity layers are revealed in the mantle transition zone, one directly above the 410-km seismic discontinuity and another at a depth of 450 to 500 km. The origin of the first layer is associated with dehydration in the mantle plumes during olivine – walesite phase transformation. The increase in the S-wave velocity at the base of the second layer can explain the observations of the so-called 520-km boundary. The traditional approach to studying the structure of the crust and upper mantle is from surface waves. Receiver functions can provide higher resolution at the same depths when a combination of P- and S-wave receiver functions is used. This type of results was obtained for Fennoscandia, Kaapvaal craton, Indian shield, Central Tien Shan, Baikal rift zone, the Azores, Cape Verde Islands, and the western Mediterranean. S-receiver functions were used in the studies of the lunar crust. The joint P- and S-receiver function inversion provides robust estimates of the parameters of seismic boundaries including weak discontinuities such as the lithosphere – asthenosphere interface of cratons. The parameters determined from receiver functions include the P- to S-wave velocity ratio. In a few regions, a very high (> 2.0) velocity ratio is observed in the lower crust, probably indicating the presence of a fluid with high pore pressure. Receiver functions allow estimating the parameters of azimuthal anisotropy as a function of depth. The changes of the parameters with depth make it possible to distinguish the active anisotropy associated with recent deformations from the frozen anisotropy – the effect of the past tectonic processes.

Receiver function analyses and joint inversion with gravity data: new constraints on the Ivrea geophysical body along a high-resolution profile

2020 ◽  
Author(s):  
Matteo Scarponi ◽  
György Hetényi ◽  
Jaroslava Plomerová ◽  
Stefano Solarino ◽  
Ludovic Baron
Keyword(s):  
Receiver Function ◽  
Joint Inversion ◽  
Gravity Data ◽  
Sampling Rate ◽  
Seismic Refraction ◽  
Western Alps ◽  
Transverse Component ◽  
Reference Points ◽  
Physical Parameters ◽  
S Wave

&lt;p&gt;We collected new seismological and gravity data in the Val Sesia and Lago Maggiore regions in NW Italy to constrain the geometry and properties of the Ivrea Geophysical Body. This piece of lower Adriatic lithosphere is known to be at anomalously shallow depth along the inner arc of the Western Alps, yet existing seismological constraints (vintage seismic refraction data, local earthquake tomography) are spatially sparse. With the aim to reach higher spatial resolution in imaging the structure of the IGB, we analyze the seismological data with various receiver function approaches to map the main velocity discontinuities, followed by joint inversion with gravity data to fill the bulk properties of bodies with densities.&lt;/p&gt;&lt;p&gt;The new data acquisition consisted of two type of campaigns. For seismology, we deployed 10 broadband seismic stations (MOBNET pool, IG CAS Prague) along a linear West-East profile at 5 km spacing along Val Sesia and across the Lago Maggiore. This network continuously recorded seismic data for 27 months at 100 Hz sampling rate. For gravimetry, we compiled existing datasets and then completed the spatial gaps by relative gravity surveys, tied to absolute reference points, to achieve 1 gravity point every 1-2 km along the profile.&lt;/p&gt;&lt;p&gt;The receiver function (RF) analyses aim at detecting velocity increases with depth: primarily the Moho and the shallow IGB interfaces and their crustal reverberations (multiples), together with their potential dip by analyzing the transverse component RFs. Furthermore, we aim at investigating the sharpness of the velocity gradient across the discontinuities by analyzing the frequency dependence of the corresponding RF peaks. We aim at reproducing the observations by simple synthetic models.&lt;/p&gt;&lt;p&gt;The 2D joint inversion combines S wave velocity V&lt;sub&gt;S&lt;/sub&gt; and bulk density as physical parameters to match both the seismological and gravimetry data. The relationship between the two parameters is initially chosen from the literature, but depending on the first results the relation itself may be inverted for, considering the various high-grade metamorphic rocks observed at the surface in the area, whose properties may not align with classical V&lt;sub&gt;S&lt;/sub&gt;&amp;#8211;density equations. In conclusion, we propose new constraints on the IGB, demonstrating the advantage of using multi-disciplinary geophysical observations and improved data coverage across the study area.&lt;/p&gt;

Inversion of reflection traveltimes for transverse isotropy

Geophysics ◽  
1995 ◽  
Vol 60 (4) ◽  
pp. 1095-1107 ◽  
Author(s):  
Ilya Tsvankin ◽  
Leon Thomsen
Keyword(s):  
Wave Velocity ◽  
Vertical Velocity ◽  
Joint Inversion ◽  
Transverse Isotropy ◽  
Taylor Series Expansion ◽  
High Sensitivity ◽  
Transversely Isotropic ◽  
P Wave ◽  
S Wave ◽  
Quartic Term

In anisotropic media, the short‐spread stacking velocity is generally different from the root‐mean‐square vertical velocity. The influence of anisotropy makes it impossible to recover the vertical velocity (or the reflector depth) using hyperbolic moveout analysis on short‐spread, common‐midpoint (CMP) gathers, even if both P‐ and S‐waves are recorded. Hence, we examine the feasibility of inverting long‐spread (nonhyperbolic) reflection moveouts for parameters of transversely isotropic media with a vertical symmetry axis. One possible solution is to recover the quartic term of the Taylor series expansion for [Formula: see text] curves for P‐ and SV‐waves, and to use it to determine the anisotropy. However, this procedure turns out to be unstable because of the ambiguity in the joint inversion of intermediate‐spread (i.e., spreads of about 1.5 times the reflector depth) P and SV moveouts. The nonuniqueness cannot be overcome by using long spreads (twice as large as the reflector depth) if only P‐wave data are included. A general analysis of the P‐wave inverse problem proves the existence of a broad set of models with different vertical velocities, all of which provide a satisfactory fit to the exact traveltimes. This strong ambiguity is explained by a trade‐off between vertical velocity and the parameters of anisotropy on gathers with a limited angle coverage. The accuracy of the inversion procedure may be significantly increased by combining both long‐spread P and SV moveouts. The high sensitivity of the long‐spread SV moveout to the reflector depth permits a less ambiguous inversion. In some cases, the SV moveout alone may be used to recover the vertical S‐wave velocity, and hence the depth. Success of this inversion depends on the spreadlength and degree of SV‐wave velocity anisotropy, as well as on the constraints on the P‐wave vertical velocity.

PS Energy Imaging Condition for Microseismic Data - Part 1: Theory and Applications in 3D Isotropic Media

Geophysics ◽  
2020 ◽  
pp. 1-79
Author(s):  
Can Oren ◽  
Jeffrey Shragge
Keyword(s):  
Wave Velocity ◽  
Model Building ◽  
Velocity Model ◽  
Microseismic Monitoring ◽  
Elastic Model ◽  
S Wave ◽  
Imaging Condition ◽  
Velocity Models ◽  
Monitoring Programs ◽  
Imaging Conditions

Accurately estimating event locations is of significant importance in microseismic investigations because this information greatly contributes to the overall success of hydraulic fracturing monitoring programs. Full-wavefield time-reverse imaging (TRI) using one or more wave-equation imaging conditions offers an effective methodology for locating surface-recorded microseismic events. To be most beneficial in microseismic monitoring programs, though, the TRI procedure requires using accurate subsurface models that account for elastic media effects. We develop a novel microseismic (extended) PS energy imaging condition that explicitly incorporates the stiffness tensor and exhibits heightened sensitivity to isotropic elastic model perturbations compared to existing imaging conditions. Numerical experiments demonstrate the sensitivity of microseismic TRI results to perturbations in P- and S-wave velocity models. Zero-lag and extended microseismic source images computed at selected subsurface locations yields useful information about 3D P- and S-wave velocity model accuracy. Thus, we assert that these image volumes potentially can serve as the input into microseismic elastic velocity model building algorithms.

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