Implications of a composite source model and seismic-wave attenuation for the observed simplicity of small earthquakes and reported duration of earthquake initiation phase

1998 ◽  
Vol 88 (5) ◽  
pp. 1171-1181
Author(s):  
S. K. Singh ◽  
M. Ordaz ◽  
T. Mikumo ◽  
J. Pacheco ◽  
C. Valdés ◽  
...  
Keyword(s):  
Seismic Waves ◽  
Wave Attenuation ◽  
Source Model ◽  
P Wave ◽  
Bright Spot ◽  
Power Law Distribution ◽  
P Waves ◽  
Velocity Amplitude ◽  
Initiation Phase ◽  
Composite Source Model

Abstract An examination of P waves recorded on near-source, velocity seismograms generally shows that most small earthquakes (Mw < 2 to 3) are simple. On the other hand, larger earthquakes (Mw ≧ 4) are most often complex. The simplicity of the seismograms of Mw < 2 to 3 events may reflect the simplicity of the source (and, hence, may imply that smaller and larger earthquakes are not self-similar) or may be a consequence of attenuation of seismic waves. To test whether the attenuation is the cause, we generated synthetic P-wave seismograms from a composite circular source model in which subevent rupture areas are assumed to follow a power-law distribution. The rupture of an event is assumed to initiate at a random point on the fault and to propagate with a uniform speed. As the rupture front reaches the center of a subevent patch (all of which are circular), a P pulse is radiated that is calculated from the kinematic source model of Sato and Hirasawa (1973). Synthetic P-wave seismograms, which are all complex, are then convolved with an attenuation operator for different values of t*. The results show that the observed simplicity of small events (Mw < 2 to 3) may be entirely explained by attenuation if t* ≧ 0.02 sec. The composite source model predicts that the average time delay between the initiation of the rupture and the rupture of the largest patch, τ, scales as M01/3, such that log τ = (1/3) log M0 − 8.462. This relation is very similar to that reported by Umeda et al. (1996) between M0 and the observed time difference between the initiation of the rupture and the rupture of the “bright spot.” It roughly agrees with the relation between M0 and the duration of the initiation phase reported by Ellsworth and Beroza (1995) and Beroza and Ellsworth (1996). The relation also fits surprisingly well the data on duration of slow initial phase, tsip, and M0, reported by Iio (1995). One possible explanation of this agreement may be that the composite source model, which is essentially the “cascade” model, successfully captures the evolution of the earthquake source process and that the rupture initiation and the abrupt increase in the velocity amplitude observed on seismograms by previous researchers roughly corresponds to the rupture of the first subevent and the breaking of the largest subevent in the composite source model.

Simulation of thermoelastic waves based on the Lord-Shulman theory

Geophysics ◽  
2021 ◽  
Vol 86 (3) ◽  
pp. T155-T164
Author(s):  
Wanting Hou ◽  
Li-Yun Fu ◽  
José M. Carcione ◽  
Zhiwei Wang ◽  
Jia Wei
Keyword(s):  
Thermal Conductivity ◽  
Expansion Coefficient ◽  
Velocity Dispersion ◽  
Wave Attenuation ◽  
Splitting Method ◽  
Grazing Incidence ◽  
P Wave ◽  
Staggered Grid ◽  
Thermal Mode ◽  
P Waves

Thermoelasticity is important in seismic propagation due to the effects related to wave attenuation and velocity dispersion. We have applied a novel finite-difference (FD) solver of the Lord-Shulman thermoelasticity equations to compute synthetic seismograms that include the effects of the thermal properties (expansion coefficient, thermal conductivity, and specific heat) compared with the classic forward-modeling codes. We use a time splitting method because the presence of a slow quasistatic mode (the thermal mode) makes the differential equations stiff and unstable for explicit time-stepping methods. The spatial derivatives are computed with a rotated staggered-grid FD method, and an unsplit convolutional perfectly matched layer is used to absorb the waves at the boundaries, with an optimal performance at the grazing incidence. The stability condition of the modeling algorithm is examined. The numerical experiments illustrate the effects of the thermoelasticity properties on the attenuation of the fast P-wave (or E-wave) and the slow thermal P-wave (or T-wave). These propagation modes have characteristics similar to the fast and slow P-waves of poroelasticity, respectively. The thermal expansion coefficient has a significant effect on the velocity dispersion and attenuation of the elastic waves, and the thermal conductivity affects the relaxation time of the thermal diffusion process, with the T mode becoming wave-like at high thermal conductivities and high frequencies.

scholarly journals Local and regional P-wave spectral attenuation model for Iran

2020 ◽  
Vol 224 (1) ◽  
pp. 241-256
Author(s):  
Ehsan Moradian Bajestani ◽  
Anooshiravan Ansari ◽  
Ehsan Karkooti
Keyword(s):  
Wave Attenuation ◽  
Vertical Component ◽  
P Wave ◽  
P Waves ◽  
Attenuation Model ◽  
Hypocentral Distance ◽  
Anelastic Attenuation ◽  
Curve Versus ◽  
Path Coverage ◽  
Spectral Attenuation

SUMMARY A robust frequency-dependent local and regional P-wave attenuation model is estimated for continental paths in the Iranian Plateau. In order to calculate the average attenuation parameters, 46 337 vertical-component waveforms related to 9267 earthquakes, which are recorded at the Iranian Seismological Center (IRSC) stations, have been selected in the distance range 10–1000 km. The majority of the event's magnitudes are less than 4.5. This collection of records provides high spatial ray path coverage. Results indicate that the shape of attenuation P-wave curve versus distance is not uniform and has three distinct sections with hinges at 90 and 175 km. A trilinear model for attenuation of P-wave amplitude in the frequency range 1–10 Hz is proposed in this study. Fourier spectral amplitudes are found to decay as R−1.2 (where R is hypocentral distance), corresponding to geometric spreading within 90 km from the source. There is a section from 90 to 175 km, where the attenuation is described as R0.8, and the attenuation is described well beyond 175 km by R−1.3. Moreover, the average quality factor for Pg and Pn waves (QPg and QPn), related to anelastic attenuation is obtained as Qpg= (54.2 ± 2.6)f(1.0096±0.07) and Qpn= (306.8 ± 7.4)f (0.51±0.05). There is a good agreement between the results of the model and observations. Also, the attenuation model shows compatibility with the recent regional studies. From the results it turns out that the amplitude of P waves attenuates more rapidly in comparison with the global models in local distances.

scholarly journals Estimation of Geodynamic Properties using Seismic Techniques at a Steel Rolling Factory, Northwestern Gulf of Suez, Egypt

2020 ◽  
Vol 8 (6) ◽  
pp. 1785-1794
Keyword(s):  
Wave Velocity ◽  
Seismic Waves ◽  
Seismic Refraction ◽  
Industrial Area ◽  
P Wave ◽  
Gulf Of Suez ◽  
S Wave ◽  
P Waves ◽  
Steel Rolling ◽  
P Wave Velocity

The objective of the current investigations is to estimate the dynamic geotechnical properties necessary for evaluating the conditions of the subsurface in order to make better decisions for economic and safe designs of the proposed structures at a Steel Rolling Factory, Ataqa Industrial Area, Northwestern Gulf of Suez, Egypt. To achieve this purpose, four seismic refraction profiles were conducted to measure the velocity of primary seismic waves (P-waves) and four profiles were conducted using Multichannel Analysis of Surface Waves (MASW) technique in the same locations of refraction profiles to measure the velocity of shear waves (S-waves). SeisImager/2D Software Package was used in the analysis of the measured data. Data processing and interpretation reflect that the subsurface section in the study area consists of two layers, the first layer is a thin surface layer ranges in thickness from 1 to 4 meters with P-wave velocity ranges from 924 m/s to 1247 m/s and S-wave velocity ranges from 530 m/s to 745 m/s. The second layer has a P-wave velocity ranges from 1277 m/s to 1573 m/s and the S-wave velocity ranges from 684 m/s to 853 m/s. Geotechnical parameters were calculated for both layers. Since elastic moduli such as Poisson’s ratio, shear modulus, Young’s modulus, and bulk’s modulus were calculated. Competence scales such as material index, stress ratio, concentration index, and density gradient were calculated also. In addition, the ultimate and allowable bearing capacities

scholarly journals Okhotsk deep earthquake 24.05.2013: nature of coseismal earth’s oscillations and estimation of P-wave amplitudes at teleseismic distances

2019 ◽  
Vol 486 (2) ◽  
pp. 237-242
Author(s):  
I. P. Kuzin ◽  
L. I. Lobkovskiy ◽  
K. A. Dozorova
Keyword(s):  
Sea Of Okhotsk ◽  
Seismic Waves ◽  
P Wave ◽  
P Waves ◽  
Deep Earthquake ◽  
Epicentral Area ◽  
Seismic Stations ◽  
The Sea Of Okhotsk ◽  
Gps Observations

The results of coseismic GPS observations in the epicentral area of 2013 Sea-of- Okhotsk earthquake are presented and specific features of seismic waves amplitudes variations with distance are detected basing on the records of Russian and international seismic stations. Global propagation of P-waves for the Sea-of-Okhotsk and Bolivian (09.06.1994) earthquakes was studied and their amplitudes on teleseismic distances were estimated.

P-wave seismic attenuation by slow-wave diffusion: Effects of inhomogeneous rock properties

Geophysics ◽  
2006 ◽  
Vol 71 (3) ◽  
pp. O1-O8 ◽  
Author(s):  
José M. Carcione ◽  
Stefano Picotti
Keyword(s):  
Fluid Flow ◽  
Wave Attenuation ◽  
Fluid Pressure ◽  
Seismic Attenuation ◽  
P Wave ◽  
Rock Properties ◽  
Stratified Medium ◽  
P Waves ◽  
Low Frequencies ◽  
Attenuation Mechanism

Recent research has established that the dominant P-wave attenuation mechanism in reservoir rocks at seismic frequencies is because of wave-induced fluid flow (mesoscopic loss). The P-wave induces a fluid-pressure difference at mesoscopic-scale inhomogeneities (larger than the pore size but smaller than the wavelength, typically tens of centimeters) and generates fluid flow and slow (diffusion) Biot waves (continuity of pore pressure is achieved by energy conversion to slow P-waves, which diffuse away from the interfaces). In this context, we consider a periodically stratified medium and investigate the amount of attenuation (and velocity dispersion) caused by different types of heterogeneities in the rock properties, namely, porosity, grain and frame moduli, permeability, and fluid properties. The most effective loss mechanisms result from porosity variations and partial saturation, where one of the fluids is very stiff and the other is very compliant, such as, a highly permeable sandstone at shallow depths, saturated with small amounts of gas (around 10% saturation) and water. Grain- and frame-moduli variations are the next cause of attenuation. The relaxation peak moves towards low frequencies as the (background) permeability decreases and the viscosity and thickness of the layers increase. The analysis indicates in which cases the seismic band is in the relaxed regime, and therefore, when the Gassmann equation can yield a good approximation to the wave velocity.

Far-field pulse shapes from circular sources with variable rupture velocities

1997 ◽  
Vol 87 (5) ◽  
pp. 1288-1296
Author(s):  
Nicholas Deichmann
Keyword(s):  
Stress Drop ◽  
Seismic Moment ◽  
Total Duration ◽  
Source Model ◽  
P Wave ◽  
Far Field ◽  
Rupture Velocity ◽  
P Waves ◽  
S Waves ◽  
Rate Functions

Abstract Recently, Sato (1994) developed a simple earthquake source model of a circular rupture expanding outward from the center of a fault with constant stress drop. In contrast to previous models, the rupture velocity is allowed to vary over the duration of faulting. This model is used to synthesize apparent moment-rate functions for a three-stage source process: first, the rupture starts out with a gradually increasing velocity, then, it continues to expand uniformly until, finally, it slows to a gradual stop. Synthetic velocity seismograms are obtained from a convolution of the apparent moment-rate functions with a causal Q-operator and an appropriate instrument response. Comparisons with an example of an earthquake signal show that, in the context of the proposed model, the observed emergent P-wave onset, which is not compatible with a constant rupture velocity, can be explained by a gradually accelerating rupture front. Systematic departures from the generally expected scaling relationship between seismic moment and rupture duration are often interpreted as evidence for a dependence of stress drop on seismic moment. However, the trade-off between stress drop and rupture velocity inherent in all kinematic source models implies that such deviations can just as well be attributed to systematic variations of rupture velocity. Whereas, in general, the total duration of the far-field displacement pulse is shorter for P waves than for S waves, the model predicts that the rise time, τ1/2, of the displacement pulse should be longer for P waves than for S waves. This feature could constitute a critical test of the model and also provide a constraint on the rupture velocity.

A comparison of Heelan and exact solutions for seismic radiation from a short cylindrical charge

Geophysics ◽  
2007 ◽  
Vol 72 (2) ◽  
pp. E33-E41 ◽  
Author(s):  
Dane Peter Blair
Keyword(s):  
Seismic Waves ◽  
Blast Hole ◽  
Field Approximation ◽  
Source Model ◽  
P Wave ◽  
Cylindrical Charge ◽  
Numerical Comparison ◽  
Far Field ◽  
Full Field ◽  
Direct Pressure

A numerical comparison is made between the Heelan approximation and an exact (full-field) solution for the radiation of seismic waves at a distance [Formula: see text], produced by a short cylindrical charge in a dry borehole of radius [Formula: see text]. The explosive source model is based on direct pressure measurements within the blast hole, and its spectral output classified by a mean frequency [Formula: see text]. To generalize comparisons, this source model is incorporated within a scale-independent treatment of the Heelan and full-field solutions. If [Formula: see text] is the material P-wave velocity, then a mean dimensionless source frequency may be defined by [Formula: see text]. For sufficiently large [Formula: see text], the Heelan solution is a valid far-field approximation only, provided [Formula: see text]. However, for the present radiation model, the far-field condition is given by [Formula: see text] (approximately), which implies that the Heelan solution is never valid if [Formula: see text], irrespective of [Formula: see text]. If [Formula: see text], the Heelan solution significantly overestimates the true seismic motion, irrespective of [Formula: see text].

Poroelastic model to relate seismic wave attenuation and dispersion to permeability anisotropy

Geophysics ◽  
2000 ◽  
Vol 65 (1) ◽  
pp. 202-210 ◽  
Author(s):  
Jorge O. Parra
Keyword(s):  
Seismic Waves ◽  
Velocity Dispersion ◽  
Wave Attenuation ◽  
Test Site ◽  
Compressional Wave ◽  
P Wave ◽  
Low Velocity ◽  
Stiffness Constant ◽  
Principal Axes ◽  
Permeability Anisotropy

A transversely isotropic model with a horizontal axis of symmetry, based on the Biot and squirt‐flow mechanisms, predicts seismic waves in poroelastic media. The model estimates velocity dispersion and attenuation of waves propagating in the frequency range of crosswell and high‐resolution reverse vertical seismic profiling (VSP) (250–1250 Hz) for vertical permeability values much greater than horizontal permeability parameters. The model assumes the principal axes of the stiffness constant tensor are aligned with the axes of the permeability and squirt‐flow tensors. In addition, the unified Biot and squirt‐flow mechanism (BISQ) model is adapted to simulate cracks in permeable media. Under these conditions, the model simulations demonstrate that the preferential direction of fluid flow in a reservoir containing fluid‐filled cracks can be determined by analyzing the phase velocity and attenuation of seismic waves propagating at different azimuth and incident angles. As a result, the fast compressional wave can be related to permeability anisotropy in a reservoir. The model results demonstrate that for a fast quasi-P-wave propagating perpendicular to fluid‐filled cracks, the attenuation is greater than when the wave propagates parallel to the plane of the crack. Theoretical predictions and velocity dispersion of inter‐well seismic waves in the Kankakee Limestone Formation at the Buckhorn test site (Illinois) demonstrate that the permeable rock matrix surrounding a low‐velocity heterogeneity contains vertical cracks.

Seismic modeling of low-frequency “shadows” beneath gas reservoirs

Geophysics ◽  
2014 ◽  
Vol 79 (6) ◽  
pp. D417-D423 ◽  
Author(s):  
Elmira Chabyshova ◽  
Gennady Goloshubin
Keyword(s):  
Wave Propagation ◽  
Arrival Time ◽  
Wave Attenuation ◽  
Low Frequency ◽  
P Wave ◽  
Wave Reflections ◽  
Gas Reservoirs ◽  
P Waves ◽  
Seismic Frequencies ◽  
Time Variations

P-wave amplitude anomalies below reservoir zones can be used as hydrocarbon markers. Some of those anomalies are considerably delayed relatively to the reflections from the reservoir zone. High P-wave attenuation and velocity dispersion of the observed P-waves cannot justify such delays. The hypothesis that these amplitude anomalies are caused by wave propagation through a layered permeable gaseous reservoir is evaluated. The wave propagation through highly interbedded reservoirs suggest an anomalous amount of mode conversions between fast and slow P-waves. The converted P-waves, which propagated even a short distance as slow P-waves, should be significantly delayed and attenuated comparatively, with the fast P-wave reflections. The amplitudes and arrival time variations of conventional and converted P-wave reflections at low seismic frequencies were evaluated by means of an asymptotic analysis. The calculations confirmed that the amplitude anomalies due to converted P-waves are noticeably delayed in time relatively to fast P-wave reflections. However, the amplitudes of the modeled converted P-waves were much lower than the amplitude anomalies observed from exploration cases.

Nonlinear Rheology at Shallow Depths with Reference to the 2016 Kumamoto Earthquakes

2019 ◽  
Vol 109 (6) ◽  
pp. 2674-2690 ◽  
Author(s):  
Norman H. Sleep ◽  
Nori Nakata
Keyword(s):  
Seismic Waves ◽  
Inelastic Strain ◽  
P Wave ◽  
Seismic Velocities ◽  
P Waves ◽  
S Waves ◽  
Shallow Subsurface ◽  
Horizontal Acceleration ◽  
Normal Traction ◽  
Uppermost Layer

Abstract Strong S waves produce dynamic stresses, which bring the shallow subsurface into nonlinear inelastic failure. We examine implications of nonlinear viscous flow, which may be appropriate for shallow muddy soil, and contrast them with those of Coulomb friction within a shallow reverberating uppermost layer with low‐seismic velocities. Waves refract into essentially vertical paths at the shallow layers and produce tractions on horizontal planes. The Coulomb ratio of shear traction to lithostatic stress for S waves equals the resolved horizontal acceleration normalized to the acceleration of gravity. The ratio of dynamic vertical normal traction to lithostatic stresses is the vertical normalized acceleration from P waves. The predicted viscous inelastic strain rate in muddy soil begins at low normalized accelerations and then increases mildly and nonlinearly with increasing normalized acceleration. Failure is unaffected when P waves decrease the vertical normal traction. Seismic waves recorded at KiK‐net station KMMH16 for the 2016 Kumamoto mainshock and strong foreshock show these effects. Inelastic deformation commences at a normalized horizontal acceleration of ∼0.25 and reduces S‐ and P‐wave velocities within the uppermost ∼15  m reverberating layer. Normalized horizontal accelerations and the Coulomb stress ratio reach ∼1.25. Strong S waves arrived even when strong P waves produced vertical tension on horizontal planes. In contrast, inelastic Coulomb failure commences at a normalized horizontal acceleration equal to the effective coefficient of friction; rapid inelastic strain precludes even higher accelerations. Furthermore, horizontal planes should fail from the stresses of strong S waves during the tensional cycle of strong P waves.

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