scholarly journals Scaling of apparent stress from broadband radiated energy catalogue and seismic moment catalogue and its focal mechanism dependence

2001 ◽  
Vol 53 (10) ◽  
pp. 943-948 ◽  
Author(s):  
Z. L. Wu
Keyword(s):  
Focal Mechanism ◽  
Seismic Moment ◽  
Apparent Stress ◽  
Radiated Energy

scholarly journals The comparative analysis of 2018 Alaska earthquakes from surface wave records

2020 ◽  
Vol 2 (1) ◽  
pp. 76-84
Author(s):  
Anastasiya Fomochkina ◽  
Boris Bukchin
Keyword(s):  
Surface Wave ◽  
Focal Mechanism ◽  
Seismic Moment ◽  
Optimal Solution ◽  
Seismic Source ◽  
P Wave ◽  
Wave Spectra ◽  
Earthquake Intensity ◽  
Second Moments ◽  
First Arrival

We consider the source of an earthquake in an approximation of instant point shift dislocation. Such a source is given by its depth, the focal mechanism determined by three angles (strike, dip, and slip), and the seismic moment characterizing the earthquake intensity. We determine the source depth and focal mechanism by a systematic exploration of 4D parametric space, and seismic moment - by solving the problem of minimization of the misfit between observed and calculated surface wave spectra for every combination of all other parameters. As is well known, the focal mechanism cannot be uniquely determined from the surface wave’s amplitude spectra only. We used P-wave first arrival polarities to select the optimal solution. Ana-lyzing the surface wave spectra at shorter periods, we describe the source in an approximation of the stress glut second moments. Using these moments we determine integral estimates of the geometry, the duration of the seismic source, and rupture propagation. The results of the application of this technique for two Alaska earthquakes that occurred in 2018 (with Mw7.9 in January and with Mw7.1 in November) are presented. The possibility of the fault plane identification, which based on the obtained estimates of the focal mechanisms and second mo-ments, is analyzed for both events. Bilateral model of the source is constructed.

Source mechanism of two 1994 intermediate-depth-focus earthquakes in Guerrero, Mexico

1999 ◽  
Vol 89 (4) ◽  
pp. 1004-1018
Author(s):  
Luis Quintanar ◽  
J. Yamamoto ◽  
Z. Jiménez
Keyword(s):  
Focal Mechanism ◽  
Seismic Moment ◽  
P Wave ◽  
Focal Mechanism Solution ◽  
Medium Size ◽  
Small Contribution ◽  
Normal Faulting ◽  
Intermediate Depth ◽  
Double Couple ◽  
First Motion

Abstract In May and December 1994, two medium-size, intermediate-depth-focus earthquakes occurred in Guerrero, Mexico, eastward of the rupture area of the great Michoacan earthquake of September 19, 1985. Even though these are not major earthquakes (∼6.4 Mw), they were widely felt through central and southern Mexico, with minor damage at Zihuatanejo and Acapulco, located along the Pacific coast, and Mexico City. Both earthquakes, separated by ∼100 km, have similar focal depths and magnitudes, however, their focal mechanisms, based upon the polarities of first arrivals, show some differences. The May earthquake shows a clear normal faulting mechanism (φ = 307°, δ = 55°, λ = −108°), whereas the December earthquake mechanism solution suggests an initial thrust faulting (φ = 313°, δ = 62°, λ = 98°) process. Although previous analysis, including local and teleseismic stations, reported a normal faulting for the December earthquake, we find that modeling using the CMT focal mechanism solution fails to reproduce the first 5 sec of the observed P-wave signal at the nearest broadband station (Δ = 168 km) and the S-wave polarity at two strong ground-motion local stations (Δ = 32, 53 km); in fact, the best fit for these stations is obtained using the thrust focal mechanism calculated from the first-motion method. Seismic moment value and rupture duration time deduced from the teleseismic spectral analysis are: 2.0 × 1018 N-m and 6.9 sec for the May event; 2.8 × 1018 N-m and 7.1 sec for the December earthquake. From the inferred seismic moment, an average Δσ of ∼15 bars for both earthquakes is obtained. Inversion of teleseismic P-wave data indicates a better fit using the CMT focal mechanism solution (normal faulting) than the first-motion mechanism for both earthquakes, although the adjustment's differences are small for the May event; for this earthquake, the rupture consisted of two sources separated by ∼7 sec, starting at a depth of ∼40 km and then propagating downdip, reaching a depth of ∼60 km. The December earthquake however, released, all its energy at a depth of 50 km in two main sources separated by ∼10 sec. The non-double-couple components values are −0.004 and −0.01 for the May and December events, respectively, indicating that the December shock has a small contribution of non-double-couple radiation that could be the result of a changing mechanism. This result agrees with the hypothesis that a slab subducting at a shallower angle (our case) is associated with the existence of random subfaults with different fault orientations. From a tectonic point of view, the complexity of the December earthquake could be the result of the observed complexity of the stress distribution around 101°W and the existence of compressional events beneath the normal faulting earthquakes near the coastline. This feature permits the flexural stresses associated to the slab bending upward to become subhorizontal at the Guerrero region. We conclude that the May earthquake corresponds to a pure normal faulting, whereas the December shock is a complex event with a variable fault geometry.

Real-time monitoring of seismic moment and radiated energy

2020 ◽  
Author(s):  
Davide Scafidi ◽  
Daniele Spallarossa ◽  
Matteo Picozzi ◽  
Dino Bindi
Keyword(s):  
Real Time ◽  
Seismic Moment ◽  
P Wave ◽  
Calibration Data ◽  
S Wave ◽  
Data Set ◽  
Local Networks ◽  
Radiated Energy ◽  
The Impact ◽  
Large Earthquakes

<p>Understanding the dynamics of faulting is a crucial target in earthquake source physics (Yoo et al., 2010). To study earthquake dynamics it is indeed necessary to look at the source complexity from different perspectives; in this regard, useful information is provided by the seismic moment (M0), which is a static measure of the earthquake size, and the seismic radiated energy (ER), which is connected to the rupture kinematics and dynamics (e.g. Bormann & Di Giacomo 2011a). Studying spatial and temporal evolution of scaling relations between scaled energy (i.e., e = ER/M0) versus the static measure of source dimension (M0) can provide valuable indications for understanding the earthquake generation processes, single out precursors of stress concentrations, foreshocks and the nucleation of large earthquakes (Picozzi et al., 2019). In the last ten years, seismology has undergone a terrific development. Evolution in data telemetry opened the new research field of real-time seismology (Kanamori 2005), which targets are the rapid determination of earthquake location and size, the timely implementation of emergency plans and, under favourable conditions, earthquake early warning. On the other hand, the availability of denser and high quality seismic networks deployed near faults made possible to observe very large numbers of micro-to-small earthquakes, which is pushing the seismological community to look for novel big data analysis strategies. Large earthquakes in Italy have the peculiar characteristic of being followed within seconds to months by large aftershocks of magnitude similar to the initial quake or even larger, demonstrating the complexity of the Apennines’ faults system (Gentili and Giovanbattista, 2017). Picozzi et al. (2017) estimated the radiated seismic energy and seismic moment from P-wave signals for almost forty earthquakes with the largest magnitude of the 2016-2017 Central Italy seismic sequence. Focusing on S-wave signals recorded by local networks, Bindi et al. (2018) analysed more than 1400 earthquakes in the magnitude ranges 2.5 ≤ Mw ≤ 6.5 of the same region occurred from 2008 to 2017 and estimated both ER and M0, from which were derived the energy magnitude (Me) and Mw for investigating the impact of different magnitude scales on the aleatory variability associated with ground motion prediction equations. In this work, exploiting first steps made in this direction by Picozzi et al. (2017) and Bindi et al. (2018), we derived a novel approach for the real-time, robust estimation of seismic moment and radiated energy of small to large magnitude earthquakes recorded at local scales. In the first part of the work, we describe the procedure for extracting from the S-wave signals robust estimates of the peak displacement (PDS) and the cumulative squared velocity (IV2S). Then, exploiting a calibration data set of about 6000 earthquakes for which well-constrained M0 and theoretical ER values were available, we describe the calibration of empirical attenuation models. The coefficients and parameters obtained by calibration were then used for determining ER and M0 of a testing dataset</p>

The RAMONES Service for Rapid Assessment of Seismic Moment and Radiated Energy in Central Italy: Concepts, Capabilities, and Future Perspectives

2021 ◽  
Author(s):  
Daniele Spallarossa ◽  
Matteo Picozzi ◽  
Davide Scafidi ◽  
Paola Morasca ◽  
Chiara Turino ◽  
...  
Keyword(s):  
Seismic Moment ◽  
Rapid Assessment ◽  
Central Italy ◽  
Web Interface ◽  
S Wave ◽  
Data Set ◽  
Decomposition Approach ◽  
Peak Displacement ◽  
Radiated Energy ◽  
Attenuation Models

Abstract We present Rapid Assessment of MOmeNt and Energy Service (RAMONES), a service for disseminating through a web interface, the estimates of seismic moment (M0) and radiated energy (ER) for earthquakes occurring in central Italy with local magnitudes above 1.7. The service is based on a fully-automatic procedure developed for downloading and processing open seismological data from the European Integrated Data Archive, Italian Civil Protection repository, and Incorporated Research Institutions for Seismology (IRIS). In its actual configuration, RAMONES uses the seismic catalog generated through the event webservice of the Italian Institute of Geophysics and Volcanology (compliant with International Federation of Digital Seismograph Networks standards) to guide the data download. The concept of RAMONES is to estimate M0 and ER from features extracted directly from recordings, namely the S-wave peak displacement (PDS) and the integral of the squared velocity (IV2S) evaluated over the S-wave window at local distances. A data set composed of 6515 earthquakes recorded in central Italy between 2008 and 2018 was used to calibrate the attenuation models relating M0 to PDS and ER to IV2S, including station corrections. The calibration values for M0 and ER were extracted from the source spectra obtained by applying a decomposition approach to the Fourier amplitude spectra known as the generalized inversion technique. To test the capabilities of RAMONES, we validate the attenuation models by performing residual analysis over about 60 earthquakes occurring in 2019 that were used for the spectral decomposition analysis but not considered in the calibration phase. Since January 2020, a testing operational phase has been running, and RAMONES has analyzed about 800 earthquakes by September 2020. The distribution of the source parameters and their relevant scaling relationships are automatically computed and disseminated in the form of maps, parametric tables, figures, and reports available through the RAMONES web interface.

Far-field radiated energy scaling in elastodynamic earthquake fault models

1998 ◽  
Vol 88 (6) ◽  
pp. 1457-1465
Author(s):  
Bruce E. Shaw
Keyword(s):  
Stress Drop ◽  
Field Energy ◽  
Far Field ◽  
Apparent Stress ◽  
Fault Models ◽  
Conservation Of Energy ◽  
Rupture Length ◽  
Radiated Energy ◽  
Sequence Of Events ◽  
Wide Range

Abstract Measurements of the far-field radiated energy in very simple elastodynamic fault models is presented, and the scaling of the radiated energy with moment and rupture length is examined. The models produce a complex sequence of events having a wide range of sizes as a result of a frictional-weakening instability. Thus, radiated energy from a broad range of sizes of events can be measured. Using conservation of energy, I am able to measure the far-field energy very accurately and efficiently. I study a range of frictions, from velocity weakening to slip weakening, in order to examine the effects of the physics of the rupture source on the radiated energy. Examining the scaling of radiated energy as a function of moment and rupture length, I find differences for slip-weakening as compared to velocity-weakening friction. I find distinct differences in how the apparent stress scales with moment and also how the apparent stress divided by the stress drop scales with moment for the different frictions. Most dramatically, the apparent stress divided by the stress drop is significantly smaller for slip weakening relative to velocity weakening. This suggests that measurements of radiated energy versus moment and rupture length in earthquakes, combined with forward elastodynamic modeling, can be used to constrain possible source physics.

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