scholarly journals SOURCE PARAMETERS of STRONG EARTHQUAKES OCCURRED in the BAIKAL REGION and TRANSBAIKALIA in 2015

2021 ◽  
pp. 217-225
Author(s):  
A. Filippova ◽  
N. Gileva
Keyword(s):  
Baikal Region ◽  
Source Parameters ◽  
Seismic Hazard Assessment ◽  
Normal Fault ◽  
Baikal Rift Zone ◽  
Body Waves ◽  
Small Scale ◽  
Seismic Events ◽  
Study Region ◽  
Moment Tensors

We calculated seismic moment tensors in a double-couple approximation (focal mechanisms, scalar seismic moments, and moment magnitudes) and hypocentral depths for twenty earthquakes with Mw≥4.2 that occurred in the Baikal region and Transbaikalia in 2015. The initial data were amplitude spectra of Rayleigh and Love waves obtained from their records at the broadband seismic stations of the IRIS and the DK networks and first-motion polarities of body waves recorded at regional distances. A combination of the normal fault and strike-slip movements dominate in the sources of the major part of the study earthquakes. For the strongest of the considered seismic events (Mw≥4.6), the subvertical compression and subhorizontal tension in the SE-NW direction prevail, i.e. the tension is perpendicular to the main structures of the Baikal rift zone. The seismic events with Mw<4.6 are characterized by a more scattered orientation of compression and tension axis that could be caused, for instance, by stress redistribution in small-scale crustal blocks after stronger earthquakes. The obtained results are of great value for issues concerned with seismic hazard assessment and the development of geodynamical models of the lithosphere evolution of the study region.

scholarly journals STRONG SEISMIC EVENTS on the SOUTH-WESTERN FLANK of the BAIKAL RIFT in 2014: November 1, 2014, Кp=13.6, Mw=4.6, I0=7–8 URIK EARTHQUAKE and December 5, 2014, Кp=13.9, Mw=4.9, I0=7–8 HOVSGOL EARTHQUAKE

2020 ◽  
pp. 350-363
Author(s):  
V. Melnikova ◽  
N. Gileva ◽  
A. Seredkina ◽  
Ya. Radziminovich
Keyword(s):  
Normal Fault ◽  
Baikal Rift Zone ◽  
Strike Slip ◽  
Historical Seismicity ◽  
Seismic Events ◽  
The South ◽  
Moment Tensors ◽  
The North ◽  
Western Flank ◽  
Tectonic Position

We consider two earthquakes occurred at the south-western flank of the Baikal rift zone (BRZ): Urik, November 1, 2014 (Mwreg=4.6) and Hovsgol, December 5, 2014 (Mwreg=4.9). First of them is localized within the area of the Main Sayan fault, the second one is located at the north of the Hovsgol Lake. Seismic moment tensors (focal mechanisms, scalar seismic moments, moment magnitudes and hypocentral depths) of the study seismic events were calculated based on surface wave amplitude spectra. Earthquake hypocenters were found to be situated in the middle crust (h=14–21 km). Both events occurred under the strike-slip stress-strain field. The strike-slip was combined with a normal fault component in the source of the Urik earthquake and with a thrust fault component in the source of the Hovsgol earthquake. In both cases, shaking intensity in the nearest settlements (=42–124 km) was less than 4–5. Analysis of historical seismicity, seismological data on the Urik and Hovsgol earthquakes and the tectonic position of their sources demonstrates that the considered events are typical for the south-western flank of the BRZ and confirms the existence of the transition zone from rift structures at the central parts of the BRZ to regional compression structures in Northern Mongolia.

A teleseismic body-wave analysis of the May 1980 Mammoth Lakes, California, earthquakes

1983 ◽  
Vol 73 (2) ◽  
pp. 419-434
Author(s):  
Jeffery S. Barker ◽  
Charles A. Langston
Keyword(s):  
Body Wave ◽  
Moment Tensor ◽  
Normal Fault ◽  
Strike Slip ◽  
Body Waves ◽  
P Wave ◽  
Moment Tensors ◽  
Double Couple ◽  
The Moment ◽  
Mammoth Lakes

abstract Teleseismic P-wave first motions for the M ≧ 6 earthquakes near Mammoth Lakes, California, are inconsistent with the vertical strike-slip mechanisms determined from local and regional P-wave first motions. Combining these data sets allows three possible mechanisms: a north-striking, east-dipping strike-slip fault; a NE-striking oblique fault; and a NNW-striking normal fault. Inversion of long-period teleseismic P and SH waves for the events of 25 May 1980 (1633 UTC) and 27 May 1980 (1450 UTC) yields moment tensors with large non-double-couple components. The moment tensor for the first event may be decomposed into a major double couple with strike = 18°, dip = 61°, and rake = −15°, and a minor double couple with strike = 303°, dip = 43°, and rake = 224°. A similar decomposition for the last event yields strike = 25°, dip = 65°, rake = −6°, and strike = 312°, dip = 37°, and rake = 232°. Although the inversions were performed on only a few teleseismic body waves, the radiation patterns of the moment tensors are consistent with most of the P-wave first motion polarities at local, regional, and teleseismic distances. The stress axes inferred from the moment tensors are consistent with N65°E extension determined by geodetic measurements by Savage et al. (1981). Seismic moments computed from the moment tensors are 1.87 × 1025 dyne-cm for the 25 May 1980 (1633 UTC) event and 1.03 × 1025 dyne-cm for the 27 May 1980 (1450 UTC) event. The non-double-couple aspect of the moment tensors and the inability to obtain a convergent solution for the 25 May 1980 (1944 UTC) event may indicate that the assumptions of a point source and plane-layered structure implicit in the moment tensor inversion are not entirely valid for the Mammoth Lakes earthquakes.

scholarly journals STRONG EARTHQUAKES in the NORTH of the LAKE BAIKAL REGION (Mw=4.6–4.7) in 2015

2021 ◽  
pp. 276-290
Author(s):  
Ya. Radziminovich ◽  
V. Melnikova ◽  
N. Gileva ◽  
A. Filippova
Keyword(s):  
Lake Baikal ◽  
Baikal Region ◽  
Moment Tensor ◽  
Seismic Hazard Assessment ◽  
Normal Fault ◽  
Seismic Moment Tensor ◽  
Macroseismic Data ◽  
Strong Earthquakes ◽  
The North ◽  
Lake Baikal Region

The paper considers three relatively strong earthquakes that occurred in 2015 in the northern Lake Baikal region: July 7 Upper Akuli earthquake (Mw=4.6) with the epicenter at the headwaters of the Akuli River, and September 25 Gulonga-I (Mw=4.7) and December 13 Gulonga-II earthquakes (Mw=4.6) with the epicenters near the mountain lakes Gulonga. Instrumental and macroseismic data on these seismic events are reported. A seismic moment tensor, calculated from surface wave records, shows normal fault focal mechanisms for Upper Akuli and Gulonga-II earthquakes and strike-slip movements in the source of the Gulonga-I seismic event. The results obtained could be used in further studies of seismic zoning and seismic hazard assessment in the northern Lake Baikal region.

scholarly journals SEISMICITY of BAIKAL and TRANSBAIKALIA in 2015

2021 ◽  
pp. 129-138
Author(s):  
V. Melnikova ◽  
N. Gileva ◽  
A. Filippova ◽  
Ya. Radziminovich ◽  
E. Kobeleva
Keyword(s):  
Focal Mechanisms ◽  
P Wave ◽  
Normal Faults ◽  
Seismic Events ◽  
Study Region ◽  
Moment Tensors ◽  
North East ◽  
The North ◽  
First Arrival ◽  
Surface Wave Data

We consider the character of the seismic process in the Baikal and Transbaikalia regions in 2015. 36430 earthquakes with KR≥3 were recorded by seismic stations of permanent and temporary networks during the year due to the sharp increase of a number of seismic events at the north-east of the study region in the area of the large Muyakan seismic activation. 53 earthquakes were felt in the cities, towns and local settlements with an intensity not exceeding 6. The largest Tallaysk earthquake (KR=14.0, Mw=5.1) occurred at the North-Muya Ridge and was followed by few aftershocks. Focal mechanisms were determined for 118 seismic events from P-wave first-arrival polarities and based on seismic moment tensors inverted from the surface wave data. It has been found, that normal faults are realized in the sources of 49 % of earthquakes with the obtained focal mechanisms.

Strain to Ground Motion Conversion of DAS Data for Earthquake Magnitude and Stress Drop Determination

2021 ◽  
Author(s):  
Itzhak Lior ◽  
Anthony Sladen ◽  
Diego Mercerat ◽  
Jean-Paul Ampuero ◽  
Diane Rivet ◽  
...  
Keyword(s):  
Early Warning ◽  
Stress Drop ◽  
Source Parameters ◽  
Simulated Data ◽  
Earthquake Early Warning ◽  
Body Waves ◽  
Ocean Bottom ◽  
Correlated Noise ◽  
S Wave ◽  
Earthquake Source Parameters

&lt;p&gt;The use of Distributed Acoustic Sensing (DAS) presents unique advantages for earthquake monitoring compared with standard seismic networks: spatially dense measurements adapted for harsh environments and designed for remote operation. However, the ability to determine earthquake source parameters using DAS is yet to be fully established. In particular, resolving the magnitude and stress drop, is a fundamental objective for seismic monitoring and earthquake early warning. To apply existing methods for source parameter estimation to DAS signals, they must first be converted from strain to ground motions. This conversion can be achieved using the waves&amp;#8217; apparent phase velocity, which varies for different seismic phases ranging from fast body-waves to slow surface- and scattered-waves. To facilitate this conversion and improve its reliability, an algorithm for slowness determination is presented, based on the local slant-stack transform. This approach yields a unique slowness value at each time instance of a DAS time-series. The ability to convert strain-rate signals to ground accelerations is validated using simulated data and applied to several earthquakes recorded by dark fibers of three ocean-bottom telecommunication cables in the Mediterranean Sea. The conversion emphasizes fast body-waves compared to slow scattered-waves and ambient noise, and is robust even in the presence of correlated noise and varying wave propagation directions. Good agreement is found between source parameters determined using converted DAS waveforms and on-land seismometers for both P- and S-wave records. The demonstrated ability to resolve source parameters using P-waves on horizontal ocean-bottom fibers is key for the implementation of DAS based earthquake early warning, which will significantly improve hazard mitigation capabilities for offshore and tsunami earthquakes.&lt;/p&gt;

Seismic doublets and a complex seismic sequence controlled by the rotation of the Juan Fernández microplate

2021 ◽  
Author(s):  
Simone Cesca ◽  
Carla Valenzuela Malebrán ◽  
José Ángel López-Comino ◽  
Timothy Davis ◽  
Carlos Tassara ◽  
...  
Keyword(s):  
Source Parameters ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Joint Analysis ◽  
Seismic Sequence ◽  
Local Data ◽  
Study Region ◽  
Coulomb Stress Changes ◽  
Earthquake Source Parameters ◽  
Stress Changes

&lt;p&gt; A complex seismic sequence took place in 2014 at the Juan Fern&amp;#225;ndez microplate, a small microplate located between Pacific, Nazca and Antarctica plates. Despite the remoteness of the study region and the lack of local data, we were able to resolve earthquake source parameters and to reconstruct the complex seismic sequence, by using modern waveform-based seismological techniques. The sequence started with an exceptional Mw 7.1-6.7 thrust &amp;#8211; strike slip earthquake doublet, the first subevent being the largest earthquake ever recorded in the region and one of the few rare thrust earthquakes in a region otherwise characterized by normal faulting and strike slip earthquakes. The joint analysis of seismicity and focal mechanisms suggest the activation of E-W and NE-SW faults or of an internal curved pseudofault, which is formed in response to the microplate rotation, with alternation of thrust and strike-slip earthquakes. Seismicity migrated Northward in its final phase, towards the microplate edge, where a second doublet with uneven focal mechanisms occurred. The sequence rupture kinematics is well explained by Coulomb stress changes imparted by the first subevent. Our analysis show that compressional stresses, which have been mapped at the northern boundary of the microplate, but never accompanied by large thrust earthquakes, can be accommodated by the rare occurrence of large, impulsive, shallow thrust earthquakes, with a considerable tsunamigenic potential.&lt;/p&gt;

A Frequency-Domain-Based Algorithm for Detecting Microseismicity Using Dense Surface Seismic Arrays

2021 ◽  
Author(s):  
Maria Mesimeri ◽  
Kristine L. Pankow ◽  
James Rutledge
Keyword(s):  
Frequency Domain ◽  
Detection Method ◽  
Maximum Amplitude ◽  
High Energy ◽  
Aftershock Sequence ◽  
Anthropogenic Activity ◽  
Small Scale ◽  
Seismic Events ◽  
Small Magnitude ◽  
Seismic Arrays

ABSTRACT We propose a new frequency-domain-based algorithm for detecting small-magnitude seismic events using dense surface seismic arrays. Our proposed method takes advantage of the high energy carried by S waves, and approximate known source locations, which are used to rotate the horizontal components to obtain the maximum amplitude. By surrounding the known source area with surface geophones, we achieve a favorable geometry for locating the detected seismic events with the backprojection method. To test our new detection method, we used a dense circular array, consisting of 151 5 Hz three-component geophones, over a 5 km aperture that was in operation at the Utah Frontier Observatory for Research in Geothermal Energy (FORGE) in southcentral Utah. We apply the new detection method during a small-scale test injection phase at FORGE, and during an aftershock sequence of an Mw 4.1 earthquake located ∼30  km north of the geophone array, within the Black Rock volcanic field. We are able to detect and locate microseismic events (Mw&lt;0) during injections, despite the high level of anthropogenic activity, and several aftershocks that are missing from the regional catalog. By comparing our method with known algorithms that operate both in the time and frequency domain, we show that our proposed method performs better in the case of the FORGE injection monitoring, and equally well for the off-array aftershock sequence. Our new method has the potential to improve microseismic event detections even in extremely noisy environments, and the proposed location scheme serves as a direct discriminant between true and false detections.

scholarly journals Triplicated P-wave measurements for waveform tomography of the mantle transition zone

Solid Earth ◽  
2012 ◽  
Vol 3 (2) ◽  
pp. 339-354 ◽  
Author(s):  
S. C. Stähler ◽  
K. Sigloch ◽  
T. Nissen-Meyer
Keyword(s):  
Transition Zone ◽  
Epicentral Distance ◽  
Body Wave ◽  
Source Parameters ◽  
Body Waves ◽  
P Wave ◽  
Theoretical Modelling ◽  
Finite Frequency ◽  
Mantle Transition Zone ◽  
Band Limited

Abstract. Triplicated body waves sample the mantle transition zone more extensively than any other wave type, and interact strongly with the discontinuities at 410 km and 660 km. Since the seismograms bear a strong imprint of these geodynamically interesting features, it is highly desirable to invert them for structure of the transition zone. This has rarely been attempted, due to a mismatch between the complex and band-limited data and the (ray-theoretical) modelling methods. Here we present a data processing and modelling strategy to harness such broadband seismograms for finite-frequency tomography. We include triplicated P-waves (epicentral distance range between 14 and 30°) across their entire broadband frequency range, for both deep and shallow sources. We show that is it possible to predict the complex sequence of arrivals in these seismograms, but only after a careful effort to estimate source time functions and other source parameters from data, variables that strongly influence the waveforms. Modelled and observed waveforms then yield decent cross-correlation fits, from which we measure finite-frequency traveltime anomalies. We discuss two such data sets, for North America and Europe, and conclude that their signal quality and azimuthal coverage should be adequate for tomographic inversion. In order to compute sensitivity kernels at the pertinent high body wave frequencies, we use fully numerical forward modelling of the seismic wavefield through a spherically symmetric Earth.

Sign in / Sign up

Export Citation Format

Share Document