Seismic phases of 25 April 2015 (Mw 7.8) Earthquake and 12 May 2015 (Mw 7.3) Earthquake Predicted by AK135 Model - A comparison

A strong Mw 7.8 (depth = 8.2 km) earthquake initiated ~80 km northwest of the Kathmandu on 25 April of 2015 was followed by the Mw 7.3 (depth = 15 km) earthquake on 12 May. The seismic phases of these earthquakes were predicted at Kakani, Kathmandu seismic station (27.80°N and 85.28°E) using software model AK135 . The model predicts 21 arrivals for Gorkha earthquake with first p phase arriving at incident angle 82.65° in 11.516 seconds and final phase SKIKSSKIKS in 3270.791 seconds with incident angle 0.02°. Similarly, for the Dolakha earthquake 27 arrivals are predicted with the first arrival p phase at incident angle 74.35° in 14.504 seconds and final arrival SKIKSSKIKS phase at incident angle 0.03° in 3268.823 seconds. The 5 depth phases and 8 core phases predicted are similar for both the earthquakes while 8 and 12 mantle phases are predicted for Gorkha earthquake and Dolakha earthquake respectively. In addition, two crustal phases (Pn, Sn) were predicted only for Dolakha earthquake. The additional phases are critically refracted seismic phases indicating the existence of the Moho discontinuity between the crust and upper mantle. Their existence for Dolakha earthquake could be the indication of different geological provinces of the source region of the earthquakes, differing in age, crustal thickness, temperature, and tectonic stress. The ratio of P wave ad S wave velocity is found to be 1.67 for the regions. These seismic phases reflect their sensitivity to different layers of the earth and carry information about the geometrical and physical properties of discontinuities inside the earth.

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Constraints on the composition of the crust and uppermost mantle in northwestern Canada: Vp/Vs variations along Lithoprobe's SNorCLE transect

Canadian Journal of Earth Sciences ◽

10.1139/e05-028 ◽

2005 ◽

Vol 42 (6) ◽

pp. 1205-1222 ◽

Cited By ~ 34

Author(s):

Gabriela Fernández-Viejo ◽

Ron M Clowes ◽

J Kim Welford

Keyword(s):

Wave Velocity ◽

Upper Mantle ◽

Laboratory Data ◽

High Ratio ◽

P Wave ◽

S Wave ◽

Uppermost Mantle ◽

Crust And Upper Mantle ◽

Slave Craton ◽

Crustal Composition

Shear-wave seismic data recorded along four profiles during the SNoRE 97 (1997 Slave Northern Cordillera Refraction Experiment) refraction wide-angle reflection experiment in northwestern Canada are analyzed to provide S-wave velocity (Vs) models. These are combined with previous P-wave velocity (Vp) models to produce cross sections of the ratio Vp/Vs for the crust and upper mantle. The Vp/Vs values are related to rock types through comparisons with published laboratory data. The Slave craton has low Vp/Vs values of 1.681.72, indicating a predominantly silicic crustal composition. Higher values (1.78) for the Great Bear and eastern Hottah domains of the Wopmay orogen imply a more mafic than average crustal composition. In the western Hottah and Fort Simpson arc, values of Vp/Vs drop to ∼1.69. These low values continue westward for 700 km into the Foreland and Omineca belts of the Cordillera, providing support for the interpretation from coincident seismic reflection studies that much of the crust from east of the Cordilleran deformation front to the Stikinia terrane of the Intermontane Belt consists of quartzose metasedimentary rocks. Stikinia shows values of 1.781.73, consistent with its derivation as a volcanic arc terrane. Upper mantle velocity and ratio values beneath the Slave craton indicate an ultramafic peridotitic composition. In the Wopmay orogen, the presence of low Vp/Vs ratios beneath the Hottah Fort Simpson transition indicates the presence of pyroxenite in the upper mantle. Across the northern Cordillera, low Vp values and a moderate-to-high ratio in the uppermost mantle are consistent with the region's high heat flow and the possible presence of partial melt.

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The Australian Plate and underlying mantle from waveform tomography with massive datasets

10.5194/egusphere-egu21-5272 ◽

2021 ◽

Author(s):

Janneke de Laat ◽

Sergei Lebedev ◽

Bruna Chagas de Melo ◽

Nicolas Celli ◽

Raffaele Bonadio

Keyword(s):

Structural Information ◽

Azimuthal Anisotropy ◽

P Wave ◽

Depth Range ◽

S Wave ◽

Crust And Upper Mantle ◽

Southern Boundary ◽

Velocity Anomaly ◽

Australian Plate ◽

Australian Continent

We present a new S-wave velocity tomographic model of the Australian Plate, Aus21.&#160; It is constrained by waveforms of 0.9 million seismograms with both the corresponding sources and stations located within the half-hemisphere centred at the Australian continent. Waveform inversion extracts structural information from surface, S- and multiple S-waves on the seismograms in the form of a set of linear equations. These equations are then combined in a large linear system and inverted jointly to obtain a tomographic model of S- and P-wave speeds and S-wave azimuthal anisotropy of the crust and upper mantle. The model has been validated by resolution tests and, for particular locations in Australia with notable differences with previous models, by independent inter-station measurements of surface-wave phase velocities, which we performed using available array data.&#160;&#160;Aus21 offers new insights into the structure and evolution of the Australian Plate and its boundaries. The Australian cratonic lithosphere occupies nearly all of the western and central Australia but shows substantial lateral heterogeneity. It extends up to the northern edge of the plate, where it is colliding with island arcs, without subducting. The rugged eastern boundary of the cratonic lithosphere provides a lithospheric definition of the Tasman Line. The thin, warm lithosphere below the eastern part of the continent, east of the Tasman Line, underlies the Cenozoic volcanism locations in the area. The lithosphere is also thin and warm below much of the Tasman Sea, underlying the Lord Howe hotspot and the submerged part of western Zealandia. A low velocity anomaly that may indicate the single source of the Lord Howe and Tasmanid hotspots is observed in the transition zone offshore the Australian continent, possibly also sourcing the East Australia hotspot. Another potential hotspot source is identified below the Kermadec Trench, causing an apparent slab gap in the overlying slab and possibly related to the Samoa Hotspot to the north. Below a portion of the South East Indian Ridge (the southern boundary of the Australian Plate) a pronounced high velocity anomaly is present in the 200-400 km depth range just east of the Australian-Antarctic Discordance (AAD), probably linked to the evolution of this chaotic ridge system.

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Direct vector-field method to obtain angle-domain common-image gathers from isotropic acoustic and elastic reverse time migration

Geophysics ◽

10.1190/geo2010-0314.1 ◽

2011 ◽

Vol 76 (5) ◽

pp. WB135-WB149 ◽

Cited By ~ 65

Author(s):

Qunshan Zhang ◽

George A. McMechan

Keyword(s):

Direct Method ◽

Incident Angle ◽

Field Method ◽

Propagation Direction ◽

P Wave ◽

Common Source ◽

Spatial Gradient ◽

Reverse Time ◽

S Wave ◽

Time Migration

We have developed an alternative (new) method to produce common-image gathers in the incident-angle domain by calculating wavenumbers directly from the P-wave polarization rather than using the dominant wavenumber as the normal to the source wavefront. In isotropic acoustic media, the wave propagation direction can be directly calculated as the spatial gradient direction of the acoustic wavefield, which is parallel to the wavenumber direction (the normal to the wavefront). Instantaneous wavenumber, obtained via a novel Hilbert transform approach, is used to calculate the local normal to the reflectors in the migrated image. The local incident angle is produced as the difference between the propagation direction and the normal to the reflector. By reordering the migrated images (over all common-source gathers) with incident angle, common-image gathers are produced in the incident-angle domain. Instantaneous wavenumber takes the place of the normal to the reflector in the migrated image. P- and S-wave separations allow both PP and PS common-image gathers to be calculated in the angle domain. Unlike the space-shift image condition for calculating the common-image gather in angle domain, we use the crosscorrelation image condition, which is substantially more efficient. This is a direct method, and is less dependent on the data quality than the space-shift method. The concepts were successfully implemented and tested with 2D synthetic acoustic and elastic examples, including a complicated (Marmousi2) model that illustrates effects of multipathing in angle-domain common-image gathers.

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Seismic Attenuation Tomography From 2018 Lombok Earthquakes, Indonesia

Frontiers in Earth Science ◽

10.3389/feart.2021.639692 ◽

2021 ◽

Vol 9 ◽

Author(s):

Awali Priyono ◽

Andri Dian Nugraha ◽

Muzli Muzli ◽

Ardianto Ardianto ◽

Atin Nur Aulia ◽

...

Keyword(s):

Wave Velocity ◽

Source Region ◽

Bouguer Anomaly ◽

High Ratio ◽

Seismic Attenuation ◽

P Wave ◽

S Wave ◽

Fluid Content ◽

P Wave Velocity ◽

Lombok Island

Local earthquake data was used to determine a three-dimensional (3D) seismic attenuation structure around the aftershock source region of the 2018 Lombok earthquake in Indonesia. The aftershocks were recorded by 13 seismic stations from August 4 to September 9, 2018. The selected data consist of 6,281 P-wave t∗ values from 914 events, which had good t∗ quality in at least four stations. Our results show that the two aftershock clusters northwest and northeast of Lombok Island have different attenuation characteristics. A low P-wave quality factor (low-Qp), low P-wave velocity (Vp), and high ratio of P-wave velocity and S-wave velocity (Vp/Vs), which coincide with a shallower earthquake (<20 km) northwest of Lombok Island, might be associated with a brittle area of basal and imbricated faults influenced by high fluid content. At the same time, the high-Qp, low Vp, and low Vp/Vs, which coincide with a deeper earthquake (>20 km) northeast of Lombok Island, might be associated with an area that lacks fluid content. The difference in fluid content between the northwest and northeast regions might be the cause of the early generation of aftershocks in the northwest area. The significant earthquake that happened on August 5, 2018, took place in a region with moderate Qp, close to the contrast of high and low-Qp and high Vp, which suggests that the earthquake started in a strong material before triggering the shallower aftershocks occurring in an area affected by fluid content. We also identified an old intrusive body on the northeast flank of the Rinjani volcano, which was characterized by a high-Qp, high-velocity, and a high Bouguer anomaly.

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Spectral analysis of body waves from the earthquake of February 18, 1956

Bulletin of the Seismological Society of America ◽

10.1785/bssa05406a2017 ◽

1964 ◽

Vol 54 (6A) ◽

pp. 2017-2035 ◽

Cited By ~ 1

Author(s):

Tomowo Hirasawa ◽

William Stauder

Keyword(s):

Amplitude Ratio ◽

Source Region ◽

Focal Depth ◽

Mean Amplitude ◽

Theoretical Models ◽

Body Waves ◽

P Wave ◽

Type I ◽

Type Ii ◽

S Wave

abstract The earthquake which occurred south of Honshu, Japan, on February 18, 1956 is studied by means of Fourier analysis. The focal depth of the shock is about 450 km and the magnitude is 714 to 712. Three theoretical models of the source mechanism, that is, Type Ia, Type Ib, and Type II, are examined by the observed amplitude spectra of S and ScS waves. It is found that the observed amplitude ratios of the Fourier components between two horizontal components of the S wave and of the ScS wave, respectively, agree well with the theoretical ratios for a Type II source. Under the assumption that spectral structures should be the same at all observing points, the scattering from the mean amplitude is calculated. The result shows that the Type II model is preferable to either of the Type I models. Assuming Honda's volume model, whose radiation pattern corresponds to that of a Type II point source, the radius of the source region is estimated by making use of the amplitude ratio of the Fourier component of the S wave to that of the P wave. The radius of the source is found to be 11 km ± 2 km.

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The Conditional Contributions of Electromagnetism and QED To Natural Hazards in Both Nano and Macro Cosmic Scales

10.5194/egusphere-egu2020-21121 ◽

2020 ◽

Author(s):

Taner Sengor

Keyword(s):

Natural Hazards ◽

Van Der Waals ◽

Vertical Direction ◽

P Wave ◽

Secondary Wave ◽

S Wave ◽

Geophysical Research ◽

Tectonic Plates ◽

The Earth ◽

Qed Effects

The Earth itself with its inwards and outwards is a unique and complete system according to all events effecting the Earth1. All the natural events involving hazards are the results of self-controlling mechanism of the complex network of this unique system. Several contributions and reports presented this fact. The classical approaches trying to explain earthquake events, say EQs, and related phenomena may be taken as approximations working for the EQs less than 5.9 Richter in magnitude according to observations coming from the application of this approach. The EQs bigger than 5.9 Richter involve very different ingredients given with dynamics based on the gravity in classical geophysics1. The ranges of (5.9+n, 5.9+n+1) for every n=1, 2, 3, ... present different formulations due to validity of the approximations and orders of the variables as relative to the energy density and frequency levels. &#160;The fact in here comes with the compactness coming with the electromagnetically equivalent models1.&#160;The planetary movements effect both the mechanics and dynamics of tectonic plates like tidal action of Pascal&#8217;s law modified with stochastic interactions. The Earth&#8217;s plates may move and collide with each other due to the forces generated by these displacements. The Primary wave comes from these mechanics of plates under planetary effects, tidal effects, and/or effects of extended Pascal&#8217;s and Archimedes&#8217; principles for compressible liquids involving non-adiabatic gasses in semi-open containers. All these effects are effective in vertical direction, totally. P wave is a result of these forces generated by the dynamics of collision of plate-to-plate, plate-to-sea, plate-to-ocean, and/or plate-to-tidal processes coming from planetary motions and acts between plates. Secondary wave come from the effects of Casimir-Polder forces and Van der Waals potentials generated by the nano-displacements occurring among touch-to-touch phases of plates just at the end of P wave phases. These QED effects are effective in horizontal direction in total iff they can generate an EQ. If the plates touch to each other with the effect of forces coming from P wave then this induces Van der Waals potentials and forces like Casimir-Polder force work on the plates generating big amount of energy then big EQs can come to truth. It is possible to model the P wave phases with the deterministic ingredients and processes; however, modelling the S wave phases are not possible without stochastic ingredients and processes. The processes like storms, typhoon, etc. developing with the atmospheric events generate the similar effects. The waves coming with EQs propagate in inflective trajectories; therefore, these waves propagate in inflective spaces. This analysis illustrates the gravity interactions of the Earth with other planets generating electromagnetic interactions in both nano-scale and quantum level in Earth&#8217;s interior as the actual trigger of EQs. The excessive fall works like the insurance for EQs preventing the occurrence of significant EQs and so, reducing the huge damage arriving from significant and/or bigger EQs.-------------------1Sengor T, &#8220;The Globally Compact Multi-Network of the Earth: the self-controlling mechanisms in natural hazards above significant level,&#8221; Geophysical Research Abstracts, Vol. 21, EGU2019-17127,2019, General Assembly 2019.

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S-Zero Stack: A converted wave processing to extract subsurface density information

Geophysics ◽

10.1190/geo2013-0029.1 ◽

2014 ◽

Vol 79 (3) ◽

pp. N1-N10

Author(s):

Keshan Zou

Keyword(s):

Incident Angle ◽

Shear Velocity ◽

P Wave ◽

Density Contrast ◽

Richards Equation ◽

Maximum Magnitude ◽

S Wave ◽

Converted Wave ◽

Amplitude Variation With Offset ◽

Conversion Point

Analyzing the Aki-Richards equation for converted waves, I found that it is possible to decouple the effect of density contrast from that of shear velocity contrast. The two terms were mixed when the P-wave incident angle was less than 30°, but they started to separate at a middle angle range (approximately 40°). The term related to S-wave velocity contrast reached zero at an incident angle around 60°. However, the other term, which was related to the density contrast, did not reverse polarity until 90°. Furthermore, this density term reached almost the maximum (magnitude) around 60°. Based on those characteristics, I designed a new method called “S-Zero Stack” to capture the density contrast reliably at the subsurface interface without going to inversion. S-Zero Stack captured subsurface density anomalies using a special stacking method. It is simple but robust, even when there is noise in the common-conversion-point gathers. Combined with the traditional P-wave amplitude-variation-with-offset technique, S-Zero Stack of PS-waves may help discriminate commercial gas from fizz in gas sand and could be a useful tool in shale gas exploration to locate lower-density anomalies (sweet spots).

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A simple model of the crust and upper mantle in central Chile

Bulletin of the Seismological Society of America ◽

10.1785/bssa0630030819 ◽

1973 ◽

Vol 63 (3) ◽

pp. 819-825

Author(s):

L. Chuaqui

Keyword(s):

Wave Velocity ◽

Upper Mantle ◽

Structural Parameters ◽

P Wave ◽

S Wave ◽

Crust And Upper Mantle ◽

Central Chile ◽

Arrival Times ◽

P Wave Velocity ◽

Wave Arrival

abstract A simplified model of the crust and upper mantle of central Chile is developed with P- and S-wave arrival times and is compared with previous gravimetric work on the area. The following structural parameters were determined: crustal P-wave velocity, upper mantle P-wave velocity, crustal thickness and orientation of the plane separating crust and upper mantle. The model obtained here agrees well with those calculated in the gravimetric study.

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Linearized Frequency-Dependent Reflection Coefficient and Attenuated Anisotropic Characteristics of Q-VTI Model

Energies ◽

10.3390/en14248506 ◽

2021 ◽

Vol 14 (24) ◽

pp. 8506

Author(s):

Yahua Yang ◽

Xingyao Yin ◽

Bo Zhang ◽

Danping Cao ◽

Gang Gao

Keyword(s):

Reflection Coefficient ◽

Seismic Wave ◽

Incident Angle ◽

Transversely Isotropic ◽

P Wave ◽

Reference Frequency ◽

Quality Factors ◽

S Wave ◽

Reservoir Properties ◽

Simultaneous Inversion

Seismic wave exhibits the characteristics of anisotropy and attenuation while propagating through the fluid-bearing fractured or layered reservoirs, such as fractured carbonate and shale bearing oil or gas. We derive a linearized reflection coefficient that simultaneously considers the effects of anisotropy and attenuation caused by fractures and fluids. Focusing on the low attenuated transversely isotropic medium with a vertical symmetry axis (Q-VTI) medium, we first express the complex stiffness tensors based on the perturbation theory and the linear constant Q model at an arbitrary reference frequency, and then we derive the linearized approximate reflection coefficient of P to P wave. It decouples the P- and S-wave inverse quality factors, and Thomsen-style attenuation-anisotropic parameters from complex P- and S-wave velocity and complex Thomsen anisotropic parameters. By evaluating the reflection coefficients around the solution point of the interface of two models, we analyze the characteristics of reflection coefficient vary with the incident angle and frequency and the effects of different Thomsen anisotropic parameters and attenuation factors. Moreover, we realize the simultaneous inversion of all parameters in the equation using an actual well log as a model. We conclude that the derived reflection coefficient may provide a theoretical tool for the seismic wave forward modeling, and again it can be implemented to predict the reservoir properties of fractures and fluids based on diverse inversion methods of seismic data.

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