Crustal and Uppermost Mantle Structure Across Central Myanmar by Joint Analysis of Receiver Functions and Rayleigh-wave Dispersion

2020 ◽  
Author(s):  
Yiming Bai ◽  
Yumei He ◽  
Xiaohui Yuan ◽  
Myo Thant ◽  
Kyaing Sein ◽  
...  
Keyword(s):  
Phase Velocity ◽  
Rayleigh Wave ◽  
Velocity Structure ◽  
Wave Dispersion ◽  
Receiver Functions ◽  
P Wave ◽  
Central Basin ◽  
Automatic Frequency ◽  
Uppermost Mantle ◽  
Rayleigh Wave Dispersion

<p>The territory of Myanmar, situated at the eastern flank of the India-Asia collision zone, is characterized by complex tectonic structure and high seismicity. From west to east, this region consists of three nearly NS-trending tectonic units: the Indo-Burma Ranges, the Central Basin and the Shan Plateau. Detailed structure of the crust and uppermost mantle beneath Myanmar can provide crucial constraints on regional tectonics, subduction dynamics as well as seismic hazard assessment. Yet seismic velocity structure beneath this region is poorly determined due to sparse regional seismic networks.</p><p>In this study, we utilize seismic data recorded at 80 broadband stations in Myanmar, among which 70 stations were deployed in 2016 under the project of China-Myanmar Geophysical Survey in the Myanmar Orogen (CMGSMO), 9 stations are operated by IRIS and the remaining one is from GEOFON. We measured the Rayleigh-wave phase velocity dispersion from the ambient noise cross-correlations at periods between 5 s and 40 s by using the automatic frequency-time analysis (AFTAN). A fast marching surface wave tomography (FMST) approach was then adopted to invert the 2-D phase velocity maps in the study region. Our preliminary results show variable crustal structure across central Myanmar, with a strong low-velocity zone north of 22°N in the Indo-Burma Ranges. Since Rayleigh-wave dispersion is more sensitive to absolute velocity speed than to velocity contrasts, the ongoing study jointly inverts the dispersion data with P-wave receiver functions to better determine the velocity discontinuities and thus provides tighter constraints on the shear-velocity structure beneath central Myanmar.</p>

Repeatability of multimode Rayleigh‐wave dispersion studies

Geophysics ◽  
2003 ◽  
Vol 68 (3) ◽  
pp. 782-790 ◽  
Author(s):  
Kristen S. Beaty ◽  
Douglas R. Schmitt
Keyword(s):  
Rayleigh Wave ◽  
Velocity Structure ◽  
Wave Dispersion ◽  
Dispersion Curves ◽  
P Wave ◽  
Surface Wave Dispersion ◽  
Near Surface ◽  
Density Values ◽  
Early Fall ◽  
Rayleigh Wave Dispersion

Rayleigh‐wave dispersion is used to study the near‐surface elastic properties of a thick, lacustrine clay to approximately 10 m depth. Ten repeated sets of Rayleigh dispersion curves were obtained through late spring to early fall. A variety of methodologies were used to extract the dispersion curves, but a modified frequency–ray parameter (f − p) method most successfully yields dispersion curves for the first three Rayleigh modes. The Rayleigh‐wave velocities varied from 100 to ∼350 m/s with frequency over the band from 75 to 10 Hz. Over this band, these velocities did not measurably vary during the study period. The observed phase velocity curves were inverted with P‐wave and density values obtained from shallow coring to obtain the shear‐wave velocity structure at the site down to > 14 m. This case study highlights the robust, repeatable, nature of surface wave dispersion methods when care is taken in the acquisition of field data.

Robust determination of S-wave velocity profiles by using mini-arrays

2020 ◽  
Author(s):  
Luca D'Auria ◽  
Marina Alfaro Rodríguez ◽  
Daniel Bermejo López ◽  
Jemma Crowther ◽  
Lucy Kennett ◽  
...  
Keyword(s):  
Inverse Problem ◽  
Rayleigh Wave ◽  
Velocity Structure ◽  
Joint Inversion ◽  
Geophysical Methods ◽  
Wave Dispersion ◽  
Dispersion Curves ◽  
P Wave ◽  
Rayleigh Wave Dispersion

<p>Microtremor measurements represent a useful tool to study the seismic amplification in urban areas. One of the methods that permits characterizing seismic properties of soils is the H/V spectral ratio. This technique is especially useful when dealing with shallow low velocity layers, allowing an effective determination of its velocity and thickness. The H/V technique is very convenient to realize microzonation surveys because of its simplicity and low cost. However, it is recommended to combine it with other geophysical methods and geological information to better constrain the resulting models. In recent years the use of ambient noise cross-correlation has been widely used to retrieve Rayleigh wave dispersion curves between pairs of stations. These curves carry an important information about the subsoil velocity structure and have been already exploited for seismic microzonation purposes.</p><p>The aforementioned methods, H/V spectra and Rayleigh wave dispersion curves, in principle allow obtaining 1D body wave and density profiles. However, one of the most important problems when inverting H/V and dispersion curves, is the poor constraint on density and P wave velocities. This difficulty can be partially solved by imposing some constraints over the inverse problem (e.g. fixing the Vp/Vs ratio) or by devising inverse methods allowing the different parameters to be determined in different steps.</p><p>We propose a novel approach which consists of a joint inversion of H/V spectra and Rayleigh wave dispersion curves, realized simultaneously for all the elements of the mini-array. This allows increasing the ratio between the number of available data and the number of parameters to invert, improving the stability of the inverse problem and reducing the uncertainties on the estimated parameters. For the evaluation of the retrieved model, we used the trans-dimensional Monte Carlo exploration which has shown to be very efficient in evaluating the quality of the resulting model, through an intensive exploration of the “a posteriori” probability density function over the model parameter space.</p><p>We show the improvement in the obtained results on synthetic tests as well as on actual data. In particular we apply this method, named method <strong>MARISMA</strong> (<strong>M</strong>ini <strong>AR</strong>rays for se<strong>IS</strong>mic <strong>M</strong>icrozon<strong>A</strong>tion) on a dataset recorded in the town of San Cristóbal de La Laguna (Tenerife, Canary Islands, Spain) during the summer of 2019.</p>

scholarly journals Shear-wave velocity structure at Mt. Etna from inversion of Rayleigh-wave dispersion patterns (2 s < T < 20 s)

2010 ◽  
Vol 53 (2) ◽  
Author(s):  
Luigia Cristiano ◽  
Simona Petrosino ◽  
Gilberto Saccorotti ◽  
Matthias Ohrnberger ◽  
Roberto Scarpa
Keyword(s):  
Rayleigh Wave ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Velocity Structure ◽  
Wave Dispersion ◽  
Dispersion Patterns ◽  
Mt Etna ◽  
Rayleigh Wave Dispersion ◽  
Shear Wave Velocity Structure

Leaking modes and the PL phase

1960 ◽  
Vol 50 (2) ◽  
pp. 165-180
Author(s):  
Jack Oliver ◽  
Maurice Major
Keyword(s):  
Rayleigh Wave ◽  
Rayleigh Waves ◽  
Wave Train ◽  
Wave Dispersion ◽  
P Wave ◽  
Wave Guide ◽  
Mode Propagation ◽  
Near Surface ◽  
Surface Particle ◽  
Rayleigh Wave Dispersion

ABSTRACT The PL phase is a normally dispersed train of waves of periods greater than about 10 seconds beginning at or near the time of the initial P wave and sometimes continuing at least to the time of the beginning of the Rayleigh-wave train. With adequate instrumentation the PL phase is commonly observed at distances less than about 25° from shallow shocks. In general, surface particle motion is elliptical and progressive, and amplitudes are not greater than about one-quarter those of Rayleigh waves of the same period. Comparison of PL- and Rayleigh-wave dispersion shows that both waves propagate in roughly the same near-surface wave guide. Whereas Rayleigh waves correspond to normal- (nonleaking-) mode propagation, PL waves appear to correspond to leakingmode propagation within this wave guide.

Seismic structure across central Myanmar from joint inversion of receiver functions and Rayleigh wave dispersion

2021 ◽  
pp. 229068
Author(s):  
Yiming Bai ◽  
Yumei He ◽  
Xiaohui Yuan ◽  
Frederik Tilmann ◽  
Yinshuang Ai ◽  
...  
Keyword(s):  
Rayleigh Wave ◽  
Joint Inversion ◽  
Wave Dispersion ◽  
Receiver Functions ◽  
Seismic Structure ◽  
Rayleigh Wave Dispersion
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