Moment magnitude estimates for central Anatolian earthquakes using coda waves

Abstract. A proper estimate of moment magnitude, which is a physical measure of the energy released at an earthquake source, is essential for better seismic hazard assessments in tectonically active regions. Here a coda wave modeling approach that enables the source displacement spectrum modeling of the examined event was used to estimate moment magnitudes of central Anatolia earthquakes. To achieve this aim, three-component waveforms of local earthquakes with magnitudes 2.0≤ML≤5.2 recorded at 69 seismic stations, which were operated between 2013 and 2015 within the framework of the Continental Dynamics–Central Anatolian Tectonics (CD–CAT) passive seismic experiment, were utilized. An inversion on the coda wave traces of each selected single event in the database was performed in five different frequency bands between 0.75 and 12 Hz. The resultant moment magnitudes (Mw coda) exhibit a good agreement with routinely reported local magnitude (ML) estimates for the study area. Apparent move-out that is particularly significant around the scattered variation of ML–Mw coda data points for small earthquakes (ML < 3.5) can be explained by possible biases of wrong assumptions to account for anelastic attenuation and seismic recordings with a finite sampling interval. Finally, I present an empirical relation between Mw coda and ML for central Anatolian earthquakes.

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Moment magnitude estimates for Central Anatolian earthquakes using coda waves

10.5194/se-2019-8 ◽

2019 ◽

Author(s):

Tuna Eken

Keyword(s):

Empirical Relation ◽

Active Regions ◽

Moment Magnitude ◽

Central Anatolia ◽

Coda Wave ◽

Seismic Experiment ◽

Tectonically Active ◽

Passive Seismic ◽

Passive Seismic Experiment ◽

Good Agreement

Abstract. Proper estimate of moment magnitude that is a physical measure of the energy released at earthquake source is essential for better seismic hazard assessments in tectonically active regions. Here a coda wave modeling approach that enables the source displacement spectrum modeling of examined event was used to estimate moment magnitude of central Anatolia earthquakes. To achieve this aim, three component waveforms of local earthquakes with magnitudes 2.0 ≤ ML ≤ 5.2 recorded at 72 seismic stations which have been operated between 2013 and 2015 within the framework of the CD-CAT passive seismic experiment. An inversion on the coda wave traces of each selected single event in our database was performed in five different frequency bands between 0.75 and 12 Hz. Our resultant moment magnitudes (MW-coda) exhibit a good agreement with routinely reported local magnitude (ML) estimates for study area. Finally, we present an empirical relation between MW-coda and ML for central Anatolian earthquakes.

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Coda-derived moment magnitudes in central Anatolia

10.5194/egusphere-egu2020-877 ◽

2020 ◽

Author(s):

Tuna Eken

Keyword(s):

Volume Averaging ◽

Sampling Interval ◽

Seismic Attenuation ◽

Coda Waves ◽

Central Anatolia ◽

Theory Approach ◽

Anelastic Attenuation ◽

Seismic Experiment ◽

Tectonically Active ◽

Passive Seismic

A reliable representation of the energy at the earthquake source is vitally important to make reliable seismic hazard assessments in tectonically active areas. The use of coda waves, for this aim, can provide source spectra for robust moment magnitude estimates mainly due to its volume-averaging property sampling the entire focal sphere as this makes these waves insensitive to any source radiation pattern effect. In the present study, we examined local earthquakes beneath central Anatolia earthquakes with magnitudes 2.0&#8804;ML&#8804;5.2 recorded at 69 seismic stations that were operated between 2013 and 2015 within the framework of the Continental Dynamics&#8211;Central Anatolian Tectonics (CD&#8211;CAT) passive seismic experiment. The inversion scheme used here involved simultaneous modeling of source properties as well as seismic attenuation parameters in five different frequency bands between 0.75 and 12&#8201;Hz. Forward modeling of coda waves was achieved through an isotropic acoustic Radiative Transfer Theory approach. A comparison between coda derived (Mw coda) and routinely reported local (ML) magnitudes shows an overall consistency. However, apparent move-out observed around small earthquakes (ML&#8201;<&#8201;3.5) can be attributed to wrong assumptions for anelastic attenuation as well as to the use of seismic recordings with a finite sampling interval.

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Passive Seismic Tomography: 3-D imaging in tectonically active regions

Global Tectonics and Metallogeny ◽

10.1127/gtm/8/2003/205 ◽

2003 ◽

Vol 8 (1-4) ◽

pp. 205-205

Author(s):

Charles B. Archambeau

Keyword(s):

Seismic Tomography ◽

Active Regions ◽

Tectonically Active ◽

Passive Seismic

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Regional attenuation models in Central and Eastern North America using the NGA-East database

Earthquake Spectra ◽

10.1177/87552930211018704 ◽

2021 ◽

pp. 875529302110187

Author(s):

Jeff Bayless

Keyword(s):

North America ◽

Frequency Dependence ◽

Gulf Coast ◽

Site Response ◽

Epistemic Uncertainty ◽

Amplitude Spectrum ◽

Active Regions ◽

Atlantic Coastal Plain ◽

Eastern North America ◽

Anelastic Attenuation

The anelastic attenuation term found in ground motion prediction equations (GMPEs) represents the distance dependence of the effect of intrinsic and scattering attenuation on the wavefield as it propagates through the crust and contains the frequency-dependent quality factor, [Formula: see text], which is an inverse measure of the effective anelastic attenuation. In this work, regional estimates of [Formula: see text] in Central and Eastern North America (CENA) are developed using the NGA-East regionalization. The technique employed uses smoothed Fourier amplitude spectrum (FAS) data from well-recorded events in CENA as collected and processed by NGA-East. Regional [Formula: see text] is estimated using an assumption of average geometrical spreading applicable to the distance ranges considered. Corrections for the radiation pattern effect and for site response based on [Formula: see text] result in a small but statistically significant improvement to the residual analysis. Apparent [Formula: see text] estimates from multiple events are combined within each region to develop the regional models. Models are provided for three NGA-East regions: the Gulf Coast, Central North America, and the Appalachian Province. Consideration of the model uncertainties suggests that the latter two regions could be combined. There were not sufficient data to adequately constrain the model in the Atlantic Coastal Plain region. Tectonically stable regions are usually described by higher [Formula: see text] and weaker frequency dependence ([Formula: see text]), while active regions are typically characterized by lower [Formula: see text] and stronger frequency dependence, and the results are consistent with these expectations. Significantly different regional [Formula: see text] is found for events with data recorded in multiple regions, which supports the NGA-East regionalization. An inspection of two well-recorded events with data both in the Mississippi embayment and in southern Texas indicates that the Gulf Coast regionalization by Cramer in 2017 may be an improvement to that of NGA-East for anelastic attenuation. The [Formula: see text] models developed serve as epistemic uncertainty alternatives in CENA based on a literature review and a comparison with previously published models.

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Estimation of absolute stress in the hypocentral region of the 2019 Ridgecrest, California, earthquakes

10.21203/rs.3.rs-75177/v1 ◽

2020 ◽

Author(s):

Yuri Fialko

Keyword(s):

Seismic Data ◽

Plate Tectonics ◽

Active Faults ◽

Active Regions ◽

Seismogenic Zone ◽

Shear Stresses ◽

Strong Earthquakes ◽

Frictional Strength ◽

Tectonically Active ◽

Weak Fault

Abstract Strength of the upper brittle part of the Earth's lithosphere controls deformation styles in tectonically active regions, surface topography, seismicity, and the occurrence of plate tectonics, yet it remains one of the least constrained and most debated quantities in geophysics. Seismic data (in particular, earthquake focal mechanisms) have been used to infer orientation of the principal stress axes. Here I show that the focal mechanism data can be combined with information from precise earthquake locations to place robust constraints not only on the orientation, but also on the magnitude of absolute stress at depth. The proposed method uses machine learning to identify quasi-linear clusters of seismicity associated with active faults. A distribution of the relative attitudes of conjugate faults carries information about the amplitude and spatial heterogeneity of the deviatoric stress and frictional strength in the seismogenic zone. The observed diversity of dihedral angles between conjugate faults in the Ridgecrest (California, USA) area that hosted a recent sequence of strong earthquakes suggests the effective coefficient of friction of 0.4-0.6, and depth-averaged shear stresses on the order of 25-40 MPa, intermediate between predictions of the "strong" and "weak" fault theories.

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Analysis of long-term observations of the groundwater level In an aseismic region

Физика земли ◽

10.31857/s0002-33372019247-67 ◽

2019 ◽

pp. 47-67

Author(s):

A. A. Lyubushin ◽

O. S. Kazantseva ◽

A. B. Manukin

Keyword(s):

Time Series ◽

Groundwater Level ◽

Atmospheric Pressure ◽

Active Regions ◽

Sampling Interval ◽

Pressure Effects ◽

Adaptive Compensation ◽

Groundwater Level Fluctuations ◽

And Cluster Analysis

The results of the analysis of continuous precise time series of atmospheric pressure and groundwater level fluctuations in a well drilled to a depth of 400 m in the territory of Moscow are presented. The observations are remarkable in terms of their duration of more than 22 years (from February 2, 1993 to April 4, 2015) and by the sampling interval of 10 min. These long observations are suitable for exploring the stationarity of the properties of hydrogeological time series in a seismically quiet region, which is important from the methodological standpoint for interpreting the similar observations in seismically active regions aimed at earthquake prediction. Factor and cluster analysis applied to the sequence of multivariate vectors ofthe statistical properties of groundwater level time series in the successive 10-day windows after adaptive compensation for atmospheric pressure effects distinguish five different statistically significant states of the time series with the transitions between them. An attempt to geophysically interpret the revealed states is made. Two significant periods – 46 and 275 days – are established by spectral analysis of the sequence of the transitions times between the clusters.

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Passcal instrument performance during the Tibetan Plateau Passive Seismic Experiment

Bulletin of the Seismological Society of America ◽

10.1785/bssa0830061959 ◽

1993 ◽

Vol 83 (6) ◽

pp. 1959-1970

Author(s):

Thomas J. Owens ◽

George E. Randall ◽

Francis T. Wu ◽

Rongsheng Zeng

Keyword(s):

Tibetan Plateau ◽

Extreme Environments ◽

Low Frequency ◽

Rocky Mountain ◽

Spatial Density ◽

Frequency Noise ◽

The Tibetan Plateau ◽

Seismic Experiment ◽

Deep Earth Structure ◽

Passive Seismic

Summary The PASSCAL instrumentation performed very well in the Tibetan Plateau Seismic Experiment. This experiment has demonstrated the viability of recording high-quality broadband data at temporary sites in extreme environments. It also highlights some areas where further development is needed. Primarily, more effort is needed to develop more versatile triggering options for the PASSCAL instruments. Such developments could both increase the instrument's success at recording low magnitude teleseismic events for travel-time studies and save disk space when recording local events, thus further increasing the feasibility of long deployments in remote regions. Although the use of the PASSCAL instrument's calibration circuitry for sensor recentering is a valuable technique, more experience is needed in the construction of sensor pads to minimize tilt problems that require site visits to relevel the seismometer such as we experienced at a few sites in the winter. This may also lead to improved low-frequency noise levels, although signals with periods greater than 200 sec can be recovered from these sites. The most exciting aspect of the data we have collected is its broad frequency content and spatial density. We anticipate that this type of experiment will be increasingly useful in the study of lithospheric interactions as well as deep Earth structure. This data was delivered to the IRIS Data Management Center in early September 1993 and is available to the community. Two other broadband passive-seismic experiments, the Baikal Rift experiment (Gao et al. 1992) and the Rocky Mountain Front experiment (Sheehan et al. 1992) should be delivered to the IRIS DMC in the Fall of 1993 as well. Temporary broadband seismic experiments represent an extension of the permanent Global Seismic Network (GSN). We encourage the seismological community to incorporate these data into any research using GSN data in order to maximize the potential utility of this new mode of seismic recording.

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