Time Domain Waveform Inversion of Short-Period P-Waves for Nuclear Explosion Source Time Functions

1981 ◽  
Author(s):  
Larry J. Ruff
Keyword(s):  
Time Domain ◽  
Nuclear Explosion ◽  
Waveform Inversion ◽  
P Waves ◽  
Short Period

scholarly journals Broadband time domain modeling of earthquakes from Friuli, Italy

1981 ◽  
Vol 71 (4) ◽  
pp. 1215-1231
Author(s):  
John Cipar
Keyword(s):  
Time Domain ◽  
Main Shock ◽  
Waveform Inversion ◽  
High Stress ◽  
Point Sources ◽  
Domain Modeling ◽  
Long Period ◽  
Short Period ◽  
Stress Drops ◽  
Period Instruments

abstract Short-period (SP) and long-period (LP) seismograms written by the main shock and two principal aftershocks of the 1976 Friuli, Italy, earthquake sequence are modeled in the time domain using synthetic seismograms. The main shock occurred on 6 May 1976 (20h 00m, Ms = 6.5) and both aftershocks on 15 September 1976 (03h 15m, Ms = 6.0 and 09h 21m, Ms = 5.9). Source models were determined initially by trial and error and then refined using a waveform inversion program. Two point sources of radiation are required to adequately model the aftershock short-period records. For the 09h 21m aftershock, the model derived from short-period records also produces good fits to the long-period data. The seismic moment of this earthquake is found to be 0.8 to 1.0 × 1025 dyne-cm. The SP model for the 03h 15m aftershock, on the other hand, predicts long-period synthetics which do not agree with the observations. In particular, the SP moment (0.37 × 1025 dyne-cm) is about 212 times smaller than the LP moment (1 × 1025 dyne-cm). Adding a long-period component to the SP model considerably improves LP waveform and moment agreement. In the case of the main shock, a reasonable fit to the observed SP data is obtained using three point sources of radiation. However, LP synthetics computed using this model do not agree with the observations, and the SP moment (0.65 × 1025 dyne-cm) is a small fraction of the LP moment (3 to 5 × 1025 dyne-cm). Time function durations indicate that the individual events inferred from the SP records are radiated from patches of the fault having radii of 2 to 4 km and stress drops in the range 35 to 276 bars. In comparison, stress drops estimated from LP data are found to be 12 bars (main shock) and 24 bars (09h 21m aftershock). These observations suggest that the short-period instruments are sensitive to the high-frequency radiation emitted from small, high-stress drop areas on the fault plane whereas the long-period instruments record the overall motion during the earthquake.

SCATTERING OF ELASTIC WAVES FROM DEPTH‐DEPENDENT INHOMOGENEITIES

Geophysics ◽  
1976 ◽  
Vol 41 (3) ◽  
pp. 441-458 ◽  
Author(s):  
Paul G. Richards ◽  
Clint W. Frasier
Keyword(s):  
Time Domain ◽  
Elastic Waves ◽  
P Waves ◽  
Simple Method ◽  
Transmitted Waves ◽  
Short Period ◽  
Scattering Of Elastic Waves ◽  
The Time Domain ◽  
Thick Crust ◽  
Zero Frequency

We have studied scattered pulse shapes by modeling inhomogeneities as a sequence of infinitesimally thin homogeneous layers. With oblique incidence of plane P or SV waves, the reflected‐converted‐transmitted waves are obtained by taking the calculus limit for the sum of primary interactions of the incident wave with all layer boundaries. The resulting scattered waves thus present themselves naturally in the time domain. For an incident impulse, the scattered pulse shape is merely an analytic function of the depth from which scatter has taken place within the inhomogeneity. The direct application of this simple method appears to be new, and we have found it remarkably accurate when compared with methods in which higher‐order boundary interactions are also retained (i.e., Haskell methods and an adaptation in the time domain which also keeps all multiples). In specific studies of P-waves incident (up to 30 degrees away from the vertical) upon a 5 km thick crust‐mantle transition, between materials having impedance ratio 1:2.8, we find the scattered pulse shapes are given adequately by our theory, for the passband of short‐period seismometers. Indeed, the theory remains remarkably accurate even for long periods, being in error by only 8 per cent at zero frequency.

Analyzing earthquakes and hybrid events on Fogo and Brava, Cape Verde, with multiple arrays

2020 ◽  
Author(s):  
Carola Leva ◽  
Georg Rümpker ◽  
Ingo Wölbern
Keyword(s):  
Time Domain ◽  
Seismic Activity ◽  
Velocity Structure ◽  
Time Windows ◽  
Broad Band ◽  
Cape Verde ◽  
Array Analysis ◽  
P Waves ◽  
Short Period ◽  
Tectonic Earthquakes

<p>Fogo and Brava are part of the south-western chain of the Cape Verde archipelago, which is believed to originate from a mantle plume. The two islands are located about 18 km apart from each other. Only Fogo experienced historic eruptions at intervals of about 20 years, with the last eruption from November 2014 to February 2015. In contrast to Fogo, Brava shows a high seismic activity. In our study we focus on the characterization of the seismicity in the region. We employ multi-array techniques to study the seismic activity, as many events are located offshore. Additionally, arrays are well suited for the analysis of volcano-related seismic signals without clear onset of phases. From January 2017 to January 2018 we operated a network of three seismic arrays (two on Fogo, one on Brava) and seven single short-period stations (five on Fogo, two on Brava). The arrays consist of 4 broad-band and 6 short-period stations each and are shaped circularly with an aperture of approximately 700 m. We apply a time-domain array analysis to locate seismic events. This approach is computationally more expensive than a traditional f-k analysis, but allows for a higher flexibility in the selection of relevant time windows to calculate the beam energy. For the analysis in the time-domain, traces are first shifted and then cut to suitable time windows to determine the energy stack as a function of horizontal slowness.</p><p>For a single array, epicentral distances can be estimated from arrival-time differences between S- and P-waves, by assuming a suitable velocity structure. However, with two or more arrays, epicenters can be obtained directly from the intersecting beams. The technique is applied to earthquakes as well as to hybrid events. During 2017 the seismicity is clearly dominated by volcano-tectonic earthquakes, mainly originating beneath and around Brava. Additionally we observe hybrid events on Fogo, which are characterized by a transition from high (20-40 Hz) to low (1-10 Hz) frequencies. The events lack clear phases, although they often exhibit a relatively sharp onset. These features provide ideal conditions for the application of the multi-array analysis. The hybrid events originate in the Chã das Caldeiras region, a collapse scar surrounding the present-day Fogo volcano, and are likely related to rock-fall events.</p>

scholarly journals Time domain viscoelastic full waveform inversion

2017 ◽  
Vol 209 (3) ◽  
pp. 1718-1734 ◽  
Author(s):  
Gabriel Fabien-Ouellet ◽  
Erwan Gloaguen ◽  
Bernard Giroux
Keyword(s):  
Time Domain ◽  
Waveform Inversion ◽  
Full Waveform Inversion ◽  
Full Waveform

Source inversion of the 1988 Upland, California, earthquake: Determination of a fault plane for a small event

1990 ◽  
Vol 80 (3) ◽  
pp. 507-518 ◽  
Author(s):  
Jim Mori ◽  
Stephen Hartzell
Keyword(s):  
Green Function ◽  
Fault Plane ◽  
Least Squares Method ◽  
Source Area ◽  
Rupture Velocity ◽  
P Waves ◽  
Waveform Data ◽  
Empirical Green Function ◽  
Finite Fault ◽  
Short Period

Abstract We examined short-period P waves to investigate if waveform data could be used to determine which of two nodal planes was the actual fault plane for a small (ML 4.6) earthquake near Upland, California. We removed path and site complications by choosing a small aftershock (ML 2.7) as an empirical Green function. The main shock P waves were deconvolved by using the empirical Green function to produce simple far-field displacement pulses. We used a least-squares method to invert these pulses for the slip distribution on a finite fault. Both nodal planes (strike 125°, dip 85° and strike 221°, dip 40°) of the first-motion focal mechanism were tested at various rupture velocities. The southwest trending fault plane consistently gave better fitting solutions than the southeast-trending plane. We determined a moment of 4.2 × 1022 dyne-cm. The rupture velocity, and thus the source area could not be well resolved, but if we assume a reasonable rupture velocity of 0.87 times the shear wave velocity, we obtain a source area of 0.97 km2 and a stress drop of 38 bars. Choice of a southwest-trending fault plane is consistent with the trend of the nearby portion of the Transverse Ranges frontal fault zone and indicates left-lateral motion. This method provides a way to determine the fault plane for small earthquakes that have no surface rupture and no obvious trend in aftershock locations.

Comparison of time-domain SH waveform inversion strategies based on sequential low and bandpass filtered data for improved resolution in near-surface prospecting

2019 ◽  
Vol 160 ◽  
pp. 69-83 ◽  
Author(s):  
Daniel Köhn ◽  
Dennis Wilken ◽  
Denise De Nil ◽  
Tina Wunderlich ◽  
Wolfgang Rabbel ◽  
...  
Keyword(s):  
Time Domain ◽  
Waveform Inversion ◽  
Near Surface
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