Utilization of Near-Source Video and Ground Motion in the Assessment of Seismic Source Functions from Mining Explosions. Velocity Model and Depth Model of the Grefco Perlite Mine

In this article, I propose a method for estimating the magnitude [Formula: see text] at which subduction megathrust earthquakes are expected to exhibit a break in magnitude scaling of both seismic source dimensions and earthquake ground motions. The methodology is demonstrated by applying it to 79 global subduction zones defined in the literature, including Cascadia. Breakpoint magnitude is estimated from seismogenic interface widths, empirical source scaling relations, and aspect ratios of physically unbounded earthquake ruptures and their uncertainties. The concept stems from the well-established observation that source-dimension and ground motion scaling decreases for shallow continental (primarily strike-slip) earthquakes when rupture exceeds the seismogenic width of the fault. Although a scaling break for megathrust earthquakes is difficult to observe empirically, all of the instrumentally recorded historical [Formula: see text] mega-earthquakes have occurred on subduction zones with [Formula: see text] (8.1–8.9), consistent with an observed break in source scaling relations derived from these same events. The breakpoint magnitudes derived in this study can be used to constrain the magnitude at which the scaling of ground motion is expected to decrease in subduction ground motion prediction equations.

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Gaussian beam migration

Geophysics ◽

10.1190/1.1442788 ◽

1990 ◽

Vol 55 (11) ◽

pp. 1416-1428 ◽

Cited By ~ 293

Author(s):

N. Ross Hill

Keyword(s):

Gaussian Beam ◽

Wave Field ◽

Seismic Source ◽

Velocity Model ◽

Downward Continuation ◽

Gaussian Beams ◽

Seismic Velocities ◽

Migration Method ◽

Gaussian Beam Migration ◽

Lateral Variations

Just as synthetic seismic data can be created by expressing the wave field radiating from a seismic source as a set of Gaussian beams, recorded data can be downward continued by expressing the recorded wave field as a set of Gaussian beams emerging at the earth’s surface. In both cases, the Gaussian beam description of the seismic‐wave propagation can be advantageous when there are lateral variations in the seismic velocities. Gaussian‐beam downward continuation enables wave‐equation calculation of seismic propagation, while it retains the interpretive raypath description of this propagation. This paper describes a zero‐offset depth migration method that employs Gaussian beam downward continuation of the recorded wave field. The Gaussian‐beam migration method has advantages for imaging complex structures. Like finite‐difference migration, it is especially compatible with lateral variations in velocity, but Gaussian beam migration can image steeply dipping reflectors and will not produce unwanted reflections from structure in the velocity model. Unlike other raypath methods, Gaussian beam migration has guaranteed regular behavior at caustics and shadows. In addition, the method determines the beam spacing that ensures efficient, accurate calculations. The images produced by Gaussian beam migration are usually stable with respect to changes in beam parameters.

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Near-Source Simulation of Strong Ground Motion in Amatrice Downtown Including Site Effects

Geosciences ◽

10.3390/geosciences11050186 ◽

2021 ◽

Vol 11 (5) ◽

pp. 186

Author(s):

Alessandro Todrani ◽

Giovanna Cultrera

Keyword(s):

Ground Motion ◽

Site Effects ◽

Central Italy ◽

Strong Motion ◽

Seismic Source ◽

Spectral Ratio ◽

Intensity Measures ◽

Standard Spectral Ratio ◽

Heavy Damage ◽

Strong Ground

On 24 August 2016, a Mw 6.0 earthquake started a damaging seismic sequence in central Italy. The historical center of Amatrice village reached the XI degree (MCS scale) but the high vulnerability alone could not explain the heavy damage. Unfortunately, at the time of the earthquake only AMT station, 200 m away from the downtown, recorded the mainshock, whereas tens of temporary stations were installed afterwards. We propose a method to simulate the ground motion affecting Amatrice, using the FFT amplitude recorded at AMT, which has been modified by the standard spectral ratio (SSR) computed at 14 seismic stations in downtown. We tested the procedure by comparing simulations and recordings of two later mainshocks (Mw 5.9 and Mw 6.5), underlining advantages and limits of the technique. The strong motion variability of simulations was related to the proximity of the seismic source, accounted for by the ground motion at AMT, and to the peculiar site effects, described by the transfer function at the sites. The largest amplification characterized the stations close to the NE hill edge and produced simulated values of intensity measures clearly above one standard deviation of the GMM expected for Italy, up to 1.6 g for PGA.

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Strong ground motion of mine tremors: Some implications for near-source ground motion parameters

Bulletin of the Seismological Society of America ◽

10.1785/bssa0710010295 ◽

1981 ◽

Vol 71 (1) ◽

pp. 295-319

Author(s):

A. McGarr ◽

R. W. E. Green ◽

S. M. Spottiswoode

Keyword(s):

Ground Motion ◽

Source Parameters ◽

Seismic Source ◽

Shear Velocity ◽

Recording System ◽

Ground Acceleration ◽

Hypocentral Distance ◽

Earthquake Size ◽

Mine Tremors ◽

Stress Drops

abstract Ground acceleration was recorded at a depth of about 3 km in the East Rand Proprietary Mines, South Africa, for tremors with −1 ≦ ML ≦ 2.6 in the hypocentral distance range 50 m < R ≦ 1.6 km. The accelerograms typically had predominant frequencies of several hundred Hertz and peak accelerations, a, as high as 12 g. The peak accelerations show a dependence on magnitude, especially when expressed as dynamic shear-stress differences, defined as σ˜ = ρRa, where ρ is density. For the mine tremors, σ˜ varies from 2 to 500 bars and depends on magnitude according to log σ˜ = 1.40 + 0.38 · ML. Accelerograms for 12 events were digitized and then processed to determine velocity and, for seven events with especially good S/N, displacement and seismic source parameters. Peak ground velocities v ranged up to 6 cm/sec and show a well-defined dependence one earthquake size as measured by ML or by seismic moment, Mo. On the basis of regression fits to the mine data, with −0.76 ≦ ML ≦ 1.45, log Rv = 3.95 + 0.57 ML, where Rv is in cm2/sec, and log Rv = −4.68 + 0.49 log Mo. These regression lines agree excellently with the corresponding data for earthquakes of ML up to 6.4 or Mo to 1.4 × 1026 dyne-cm. At a given value of ML or Mo, a, at fixed R, shows considerably greater variation than v and appears to depend on the bandwidth of the recording system. The peak acceleration at small hypocentral distances is broadly consistent with ρRa = 1.14 Δτrofs/β, where Δτ is stress drop, ro is the source radius, β is shear velocity, and fs is the bandwidth of the recording system. The peak velocity data agree well with Rv = 0.57 βΔτro/μ, where μ is the modulus of rigidity; both expressions follow from Brune's model of the seismic source and were compared with data for events in the size range 5 × 1016 ≦ Mo ≦ 1.4 × 1026 dyne-cm. Measurements of the source parameters indicated that, as for earthquakes, the stress drops for the tremors range from 1 to 100 bars and show no consistent dependence on Mo down to Mo = 5 × 1016 dyne-cm.

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Seismic source tracking with six degree‐of‐freedom ground motion observations

Journal of Geophysical Research Solid Earth ◽

10.1029/2020jb021112 ◽

2021 ◽

Author(s):

Shihao Yuan ◽

Kilian Gessele ◽

Alice‐Agnes Gabriel ◽

Dave A. May ◽

Joachim Wassermann ◽

...

Keyword(s):

Ground Motion ◽

Seismic Source ◽

Degree Of Freedom ◽

Source Tracking ◽

Six Degree Of Freedom

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Far-offset detection of normal modes and diving waves: a case study in Valhall, southern North Sea

Geophysics ◽

10.1190/geo2021-0267.1 ◽

2021 ◽

pp. 1-50

Author(s):

Filipe Borges ◽

Martin Landrø

Keyword(s):

Normal Modes ◽

Seismic Source ◽

Velocity Model ◽

Seismic Survey ◽

The Past ◽

Lack Of Control ◽

Record Data ◽

Refracted Waves ◽

1D Velocity Model

The use of permanent arrays for continuous reservoir monitoring has become a reality in the past decades, with Ekofisk and Valhall being its flagships. One of the possibilities when such solution is available is to passively record data while acquisitions with an active source are ongoing in nearby areas. These recordings might contain ultrafar-offset data (over 30 km), which are hardly used in standard reservoir exploration and monitoring, as they are mostly a combination of normal modes, deep reflections and diving waves. We present here data from the Valhall Life of Field Seismic array, recorded while an active seismic survey was being acquired in Ekofisk, in April 2014. Despite the lack of control on source firing time and position, analysis of the data shows that the normal modes are remarkably clear, overcoming the ambient noise in the field. The normal modes can be well explained by a two-layer acoustic model, while a combination of diving waves and refracted waves can be fairly well reproduced with a regional 1D velocity model. We suggest a method to use the far-offset recordings to monitor changes in the shallow sediments between source and receivers, both with and without a coherent seismic source in the area.

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Seismic hazard maps of Peshawar District for various return periods

Natural Hazards and Earth System Science ◽

10.5194/nhess-20-1639-2020 ◽

2020 ◽

Vol 20 (6) ◽

pp. 1639-1661

Author(s):

Khalid Mahmood ◽

Naveed Ahmad ◽

Usman Khan ◽

Qaiser Iqbal

Keyword(s):

Seismic Hazard ◽

Ground Motion ◽

Target Location ◽

Epistemic Uncertainty ◽

Hazard Analysis ◽

Source Parameters ◽

Seismic Source ◽

Return Periods ◽

Hazard Maps ◽

Seismic Hazard Maps

Abstract. Probabilistic seismic hazard analysis of Peshawar District has been performed for a grid size of 0.01∘. The seismic sources for the target location are defined as the area polygon with uniform seismicity. The earthquake catalogue was developed based on the earthquake data obtained from different worldwide seismological networks and historical records. The earthquake events obtained at different magnitude scales were converted into moment magnitude using indigenous catalogue-specific regression relationships. The homogenized catalogue was subdivided into shallow crustal and deep-subduction-zone earthquake events. The seismic source parameters were obtained using the bounded Gutenberg–Richter recurrence law. Seismic hazard maps were prepared for peak horizontal acceleration at bedrock level using different ground motion attenuation relationships. The study revealed the selection of an appropriate ground motion prediction equation is crucial for defining the seismic hazard of Peshawar District. The inclusion of deep subduction earthquakes does not add significantly to the seismic hazard for design base ground motions. The seismic hazard map developed for shallow crustal earthquakes, including also the epistemic uncertainty, was in close agreement with the map given in the Building Code of Pakistan Seismic Provisions (2007) for a return period of 475 years on bedrock. The seismic hazard maps for other return periods i.e., 50, 100, 250, 475 and 2500 years, are also presented.

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Seismic hazard maps of Peshawar district for various return periods

10.5194/nhess-2019-299 ◽

2019 ◽

Author(s):

Khalid Mahmood ◽

Usman Khan ◽

Qaiser Iqbal ◽

Naveed Ahmad

Keyword(s):

Seismic Hazard ◽

Ground Motion ◽

Target Location ◽

Epistemic Uncertainty ◽

Source Parameters ◽

Seismic Source ◽

Return Periods ◽

Hazard Maps ◽

Earthquake Catalogues ◽

Seismic Hazard Maps

Abstract. The probabilistic seismic hazard analysis of Peshawar District has been conducted in for a grid size of 0.01. The seismic sources for the target location are defined as the area polygon with uniform seismicity for which, the earthquake catalogues were obtained from different worldwide seismological network data. The earthquake catalogues obtained in different magnitude scale was converted into moment magnitude using regression analysis. The homogenized catalogue was then further subdivided into shallow crustal and deep subduction zone earthquake events for which, the seismic source parameters were obtained using Bounded Gutenberg-Richter Recurrence law. The seismic hazard maps were prepared in term of PGA at bedrock using the different ground motion attenuation relationships. The study shows that; the selection of appropriate ground motion prediction equation is an important factor in deciding the seismic hazard of Peshawar District. The inclusion of deep subduction earthquake does not add significantly to the seismic hazard. The calculated seismic hazard map for shallow crustal earthquake after including the epistemic uncertainty was in close agreement to that developed by BCP-2007 for a return period of 475 years on bedrock. The seismic hazard maps for other return periods i.e., 50, 100, 250, 475 and 2500 years were then prepared.

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