scholarly journals Source parameters for the Roermond aftershocks of 1992 April 13-May 2 and site spectra for P and S waves at the Belgian seismic network

1994 ◽  
Vol 116 (3) ◽  
pp. 673-682 ◽  
Author(s):  
Mihnea-Corneliu Oncescu ◽  
Thierry Camelbeeck ◽  
Henri Martin
Keyword(s):  
Source Parameters ◽  
Seismic Network ◽  
S Waves

Current Status and Future of Regional Seismic Network Monitoring in the Central and Eastern United States

2019 ◽  
Vol 91 (2A) ◽  
pp. 660-676 ◽  
Author(s):  
John E. Ebel ◽  
Martin C. Chapman ◽  
Won-Young Kim ◽  
Mitchell Withers
Keyword(s):  
United States ◽  
Seismic Hazard ◽  
Source Parameters ◽  
Seismic Wave Propagation ◽  
Seismic Network ◽  
Current Status ◽  
Future Research ◽  
Eastern United States ◽  
The Past ◽  
Earthquake Source Parameters

Abstract The central and eastern United States (CEUS) is an area of generally low-to-moderate seismic hazard with a number of large cities with high seismic risk, a history of occasional damaging earthquakes, and seismic activity induced by wastewater disposal. Seismic monitoring in the CEUS, which began at the beginning 1900s, has undergone many changes through time. Over the past two decades, broadband digital seismic stations connected by internet communications have become widespread. Modern data processing systems to automatically locate earthquakes and assign event magnitudes in near-real time have become the norm, and, since the inception of the Advanced National Seismic System in 2000, more than 10,000 earthquakes have been located and cataloged. Continuously recorded digital seismic data at 100 samples per second are allowing new avenues of research into earthquake source parameters, ground-motion excitation, and seismic wave propagation. Unfortunately, over the past two decades the number of regional seismic network (RSN) centers has diminished due to consolidations and terminations, as funding has tightened. Nevertheless, the public in different parts of the CEUS still looks to local experts for information when earthquakes take place or when they have questions about earthquakes and seismic hazard. The current RSNs must evolve to encompass the need for local seismic information centers and to serve the needs of present and future research into the causes and effects of CEUS earthquakes.

Earthquake source properties from analysis of dynamic ruptures and far-field seismic waves in a damage-breakage model

2020 ◽  
Vol 224 (3) ◽  
pp. 1793-1810
Author(s):  
Ittai Kurzon ◽  
Vladimir Lyakhovsky ◽  
Yehuda Ben-Zion
Keyword(s):  
Seismic Waves ◽  
Source Parameters ◽  
Dominant Frequency ◽  
Earthquake Source ◽  
Corner Frequency ◽  
Far Field ◽  
Rupture Directivity ◽  
Rupture Velocity ◽  
S Waves ◽  
Dominant Frequencies

SUMMARY We present results on earthquake source properties using simulations of dynamic rupture and radiated seismic waves in a continuum damage-breakage rheological model. The source properties are derived by (1) calculation of source parameters directly from the simulated ruptures and (2) observational processing of the far-field radiated waves. The seismic potency, moment, damage-related source term, rupture velocity and effective rigidity are estimated directly from the simulated sources, while the radiation pattern, dominant frequency, directivity, rupture velocity and seismic potency are calculated through analysis of the radiated waves. The potencies calculated directly from the sources are used to validate those estimated by wave analysis. The effective rigidity at the rupture zone during failure is about four times smaller than that of the intact surrounding rocks. Rupture velocity can be estimated by far-field measurements for sources with unidirectional ruptures with prominent rupture directivity. The dominant frequencies for P and S waves $f_d^S/f_d^P$ reflect clearly the rupture duration and have a ratio in the range 0.87–1.12. Seismic potencies obtained through processing the P or S waves have an overall ±15 per cent difference from the source reference values. The calculated values of the coefficient ${\rm{\kappa }}$, relating rupture length to corner or dominant frequency, have strong dependency on the source geometry. Using a strain-rate dependent ${\rm{\kappa }}$, we obtain much weaker dependencies of strain-drop on the dominant frequencies, $\Delta {\rm{\varepsilon }} \propto {( {{f_d}} )^{3/4}}$, than the classical cube-dependency between stress drop and corner frequency, and corresponding weak dependency of average slip on dominant frequency, ${\rm{\bar{D}}} \propto {( {{f_d}} )^{1/2}}$. The obtained analysis procedure and relations can be used to reduce the uncertainty of source properties derived from far-field seismic waves.

Effect of Fixing Earthquake Depth in ShakeAlert Algorithms on Performance for Intraslab Earthquakes

2021 ◽  
Author(s):  
Mika Thompson ◽  
J. Renate Hartog ◽  
Erin A. Wirth
Keyword(s):  
Pacific Northwest ◽  
Performance Metrics ◽  
Source Parameters ◽  
Focal Depth ◽  
Warning System ◽  
Seismic Network ◽  
Shallow Depth ◽  
Earthquake Early Warning System ◽  
The Pacific ◽  
Alert Threshold

Abstract We investigate whether assuming a fixed shallow depth in the ShakeAlert network-based earthquake early warning system is sufficient to produce accurate ground-motion based alerts for intraslab earthquakes. ShakeAlert currently uses a fixed focal depth of 8 km to estimate earthquake location and magnitude. This is an appropriate way to reduce computational costs without compromising alert accuracy in California, where earthquakes typically occur on shallow crustal faults. In the Pacific Northwest (PNW), however, the most common moderate-magnitude events occur within the subducting Juan de Fuca slab at depths between ∼35 and 65 km. Using a dataset of seismic recordings from 37 Mw 4.5+ intraslab earthquakes from the PNW and Chile, we replay events through the Earthquake Point-Source Integrated Code and eqInfo2GM algorithms to estimate source parameters and compute modified Mercalli intensity (MMI) alert threshold contours. Each event is replayed twice—once using a fixed 8 km depth and a second time using the actual catalog earthquake depth. For each depth scenario, we analyze MMI III and IV contours using various performance metrics to determine the number of correctly alerted sites and measure warning times. We determine that shallow depth replays are more likely to produce errors in location estimates of greater than 50 km if the event is located outside of a seismic network. When located within a seismic network, shallow and catalog depth replays have similar epicenter estimates. Results show that applying catalog earthquake depth does not improve the accuracy of magnitude estimates or MMI alert threshold contours, or increase warning times. We conclude that using a fixed shallow earthquake depth for intraslab earthquakes will not significantly impact alert accuracy in the PNW.

Depth dependence of source parameters at Monticello, South Carolina

1983 ◽  
Vol 73 (6A) ◽  
pp. 1735-1751
Author(s):  
J. B. Fletcher ◽  
J. Boatwright ◽  
W. B. Joyner
Keyword(s):  
South Carolina ◽  
Stress Drop ◽  
Strong Dependence ◽  
Source Parameters ◽  
Failure Process ◽  
The Other ◽  
Depth Range ◽  
S Wave ◽  
S Waves ◽  
Stress Drops

Abstract Three estimates of stress differences, which include Brune stress drop, stress drop from rms of acceleration (arms), and the apparent stress, have been determined for 13 earthquakes at Monticello, South Carolina, a site of reservoir-induced seismicity. Data for nine of the events come from digitally recorded three-component seismograms at four or five stations that were deployed around the Monticello Reservoir in May and early June 1979. The data from the other four events come from a strong-motion accelerograph located on the dam abutment at the southwest end of the reservoir. Estimates of the seismic moment (Mo) range from 4.6 × 1017 to 3.4 × 1020 dyne-cm (S waves) and radiated energy from about 1011 to 3 × 1016 dyne-cm (S waves). Brune stress drops ranged from 0.5 bars to about 90 bars and show a strong dependence on depth (focal depths range from 0.07 to 1.4 km) and a moderate dependence on Mo. Arms stress drops from the direct S-wave span a similar range of values and also exhibit a strong dependence on depth. Apparent stresses are usually lower than the other estimates of stress differences by a factor of 2 to 4. Seismic stress differences are highest in the topmost 0.2 to 0.3 km, a depth range for which the in situ measurements of stress and pore pressure suggest that the rock is in a state of incipient failure. In this depth range, where the four largest events occurred, the stress drops are of the same order as the ambient shear stress. These data suggest that at Monticello, where pore fluids have a strong influence on the failure process, the largest stresses released seismically are in regions most conducive to failure and that the seismic efficiencies for events at Monticello are larger than have been reported for other tremors in different tectonic settings.

Deciphering the source parameters and genesis of the 2017, Mw 4 Montesano earthquake close to the Val d’Agri Oilfield (Italy)

2021 ◽  
Author(s):  
José Ángel López-Comino ◽  
Thomas Braun ◽  
Torsten Dahm ◽  
Simone Cesca ◽  
Stefania Danesi
Keyword(s):  
Moment Tensor ◽  
Source Parameters ◽  
Tectonic Stress ◽  
Fault System ◽  
S Waves ◽  
Hydrocarbon Reservoir ◽  
Empirical Green Function ◽  
Stress Changes ◽  
The Moment ◽  
Directivity Effects

<p>On October 27<sup>th</sup>, 2017, a M<sub>w</sub> 4 earthquake occurred close to the municipality of Montesano sulla Marcellana, less than 10 km external to the concession of the largest European on-shore hydrocarbon reservoir - the Val d’Agri oilfield (Southern Italy). Being a weak event located outside the extended monitoring domain of the industrial concession, the relevance of this earthquake and possible links with the hydrocarbon exploitation were not deepened. The study of weak to moderate earthquakes can improve the characterization of the potentially destructive seismic hazard of this particular area, already struck by M>6.5 episodes in the past. Taking advantage of a wide coverage of seismic stations deployed in the VA region, we analyze the source parameters of this M<sub>w</sub> 4 earthquake applying advanced seismological techniques to estimate the uncertainties derived from the moment tensor inversion and identify plausible directivity effects. The moment tensor is dominated by a NW-SE oriented normal faulting with a centroid depth of 14 km. A single M<sub>L</sub> 2.1 aftershock was recorded and used as empirical Green function to calculate the apparent source time function for the mainshock. Apparent durations (in the range 0.11 - 0.21 s, obtained from S-waves) define an azimuthal pattern which reveals an asymmetric bilateral rupture with the 70% of the rupture propagation in the N310°W direction, suggesting a rupture plane dipping to the SW. Our results conclude that the Montesano earthquake activated a deeper fault segment associated to the Eastern Agri Fault System close to the basement. The relative low trigger potential below 10% based on depletion-induced stress changes discards an induced or triggered event due to the long-term hydrocarbon extraction in the Val d’Agri oilfield, and it rather suggests a natural cause due to the local tectonic stress.</p>

scholarly journals ASP: An Automated Seismic Processor for microearthquake networks

1982 ◽  
Vol 72 (1) ◽  
pp. 303-325
Author(s):  
T. V. McEvilly ◽  
E. L. Majer
Keyword(s):  
High Speed ◽  
Nuclear Explosion ◽  
Source Parameters ◽  
Aftershock Sequence ◽  
P Wave ◽  
Time Analysis ◽  
S Waves ◽  
Real Time Analysis ◽  
Data Output ◽  
Cerro Prieto

abstract ASP, a low-power, in-field Automated Seismic Processor of microearthquake network data has been designed, fabricated, and deployed for initial operation in four different field areas to monitor seismicity associated with two geothermal areas (The Geysers, California, and Cerro Prieto, Mexico), a nuclear explosion with its related collapse and aftershock sequence, and late (>1 year) activity in a major aftershock series (Livermore, California). A second ASP system, with a high-speed front-end, is used in acoustic emission (1 to 20 kHz) analysis for fracture monitoring. Each of the 15 channels of ASP (configured for up to 128 channels) automatically detects, measures times and amplitudes, and computes and fits FFT's for both the P and S waves on data sampled at 100 samples/sec. These data from each channel are then processed with a central microprocessor for hypocenter location, running b values, source parameters, event count, and P-wave polarities. The system is capable of processing a 15-station detection in approximately 40 sec, excluding printout. The initial trials have demonstrated that in-field real-time analysis of data maximizes the efficiency of microearthquake surveys allowing flexibility in experimental procedures, with a minimum of the traditional labor-intensive postprocessing. Current efforts are directed toward improving efficiency of computation and data output and in expanding software capabilities.

scholarly journals SEISMICITY of the URALS and WESTERN SIBERIA in 2015

2021 ◽  
pp. 200-209
Author(s):  
A. Malovichko ◽  
R. Dyagilev ◽  
F. Verkholantsev ◽  
I. Golubeva ◽  
T. Zlobina
Keyword(s):  
Seismic Activity ◽  
Western Siberia ◽  
Source Parameters ◽  
Processing Technique ◽  
Seismic Network ◽  
The Urals ◽  
Tectonic Event ◽  
Network Capability

The article summarizes information about seismic network in the Urals and Western Siberia region, describes processing technique, presents a short analysis of the seismic activity in 2015. Seismic network capability is shown for the whole territory under control. It was found that about 82 % of registered events are explosions in mines and open pits, 37 events are natural or induced ones. For the strongest induced events, variants of source parameters obtained by different agencies are shown. The strongest tectonic event in 2015 and for the last century (after 1914) is the Middle Ural earthquake with ML=4.7, I0=6 that occurred on October 18, 2015.

Estimation of earthquakes location errors distribution for LUMINEOS local seismic network in Poland. 

2021 ◽  
Author(s):  
Jakub Kokowski ◽  
Łukasz Rudziński
Keyword(s):  
Noise Level ◽  
Velocity Model ◽  
Seismic Network ◽  
Simple Task ◽  
Detection Range ◽  
S Waves ◽  
Location Errors ◽  
Precise Knowledge ◽  
Observation Network ◽  
Copper Mines

<p>Estimation of hypocenter location errors  is not a simple task. These errors are influenced by many factors. The most important are: the quality of velocity model, the configuration of stations in the observation network and the noise level recorded at stations. While the network configuration affects the error distribution in a deterministic manner, the noise level is largely random. It means that the uncertainties cannot be determined in a deterministic way and only statistical approach can be used. There are several methods for estimating location errors for particular seismic network. Some techniques use synthetic seismograms to calculate the detection range related to each station. However, this approach requires very precise knowledge of the geological model, which is not always possible. Instead, in this work we present a different approach, which uses only phase data for events included in the catalog. In this method, the detection range for each station is estimated using the detection probability (Schorlemmer & Woessner, 2008) used for both P- and S- waves first arrivals. The usefulness of this approach is discussed assuming the shape of  LUMINEOS seismic network which operates in the Legnica-Głogów Copper District (LGCD), Poland. In the LGCD region seismic activity is related to three deep underground copper mines. Every year thousand of seismic events with magnitudes up to M4.0 are registered here. Some of them are followed by tragic mining collapses and are widely felt by local residents.</p>

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