Regional bias in estimates of earthquake MS due to surface-wave path effects

1994 ◽  
Vol 84 (2) ◽  
pp. 377-382
Author(s):  
Rachel E. Abercrombie
Keyword(s):  
Surface Wave ◽  
Tectonic Setting ◽  
High Surface ◽  
Earthquake Source ◽  
Plate Boundaries ◽  
Source Type ◽  
Shallow Earthquakes ◽  
Seismic Strain Rate ◽  
Seismic Strain ◽  
Wave Path

Abstract Continental earthquakes have long been known to have anomalously high surface-wave magnitudes relative to their seismic moments. A recent global study of shallow earthquakes by Ekström and Dziewonski (1988) confirmed this and found other regional, systematic anomalies in the MS-M0 relationship. It is important to determine the source of these anomalies in order to understand the controls on earthquake-source radiation and to obtain accurate estimates of historical seismic strain rates. In this study the magnitudes of 82 earthquakes from eight different tectonic regions are recalculated using a simple surface-wave path correction to determine whether path effects are responsible for the observed anomalies. The magnitudes of continental earthquakes are reduced by an average of 0.2 magnitude units, an improvement in fit to the global average significant at the 98% level. Surface-wave path effects are clearly responsible for the high MS observed in continental areas. There is a small decrease in scatter in the other areas, but lateral refraction of the surface waves at plate boundaries prevents the simple correction from having a significant effect. There is no evidence in the observed anomalies, however, for any dependence of earthquake-source type on tectonic setting. It is clear that to obtain reliable, unbiased estimates of regional seismic strain rate and hazard, a local moment-magnitude relationship should be preferred to a global one.

scholarly journals GEODYNAMICS AND MAGMATISM OF THE PACIFIC-TYPE TRANSFORM MARGINS. ASPECTS AND DISCRIMINANT DIAGRAMS

2021 ◽  
pp. 3-24
Author(s):  
A.V. Grebennikov ◽  
◽  
A.I. Khanchuk ◽  
Keyword(s):  
Continental Margin ◽  
Tectonic Setting ◽  
Island Arc ◽  
Igneous Rocks ◽  
High Alumina ◽  
Plate Boundaries ◽  
Spreading Ridge ◽  
Convergent Margins ◽  
Oceanic Plate ◽  
Plate Movement

Transform margins represent lithospheric plate boundaries with horizontal sliding of oceanic plate, which in time and space replaced the subduction related convergent margins. This happened due to: spreading ridge–trench intersection (California; Queen Charlotte–Northern Cordilleran, West of the Antarctic Peninsula, and probably the Late Miocene–Pleistocene Southernmost South America) or ridge death along continental margin (Baja California); change in the direction of oceanic plate movement (Western Aleutian–Komandorsk; Southernmost tip of the Andes); and island arc-continent collision (New Guinea Island). Post-subduction magmatism is related to a slab window that resulted either from the spreading ridge collision (subduction) with a continental margin or slab tear formation, or slab break-off after subduction cessation due to other reasons. Igneous magmatic series formed in consequence of these events show diversity of tholeiitic (sub-alkaline), alkaline or calc-alkaline, high-alumina and adakitic rocks. The comprehensive geochemical dataset (more than 2400 analyses) on igneous rocks of the model transform and convergent geodynamic settings allowed to substantiate the most informative triple diagrams for the petrogenic oxides TiO2 × 10 – Fe2O3Tot – MgO and trace elements Nb – La– Yb. Mostly approved for the rock compositions with SiO2 < 63 wt. %, the new plots are capable of distinguishing igneous rocks formed above zones of subduction at an island arc and continental margin (related to convergent margins), from those formed in the tectonic setting of transform margins along continents or island arcs.

Measurement of interstation phase and group velocities and Q using Wiener filtering

1982 ◽  
Vol 72 (1) ◽  
pp. 73-91
Author(s):  
Steven R. Taylor ◽  
M. Nafi Toksöz
Keyword(s):  
Surface Wave ◽  
Green’S Function ◽  
Green's Function ◽  
Amplitude Spectrum ◽  
Wiener Filter ◽  
Wave Path ◽  
Phase And Group Velocities ◽  
Filtering Technique ◽  
Surface Wave Data ◽  
Group Velocities

abstract A method for calculating interstation phase and group velocities and attenuation coefficients using a Wiener (least-squares) filtering technique is presented. The interstation Green's (or transfer) function is estimated from surface wave data from two stations laying along the same great circle path. The estimate is obtained from a Wiener filter which is constructed to estimate the signal recorded at the station further from the source from the signal recorded at the nearer station. The interstation group velocity is obtained by applying the multiple-filtering technique to the Green's function, and the interstation phase velocity from the phase spectrum of the Green's function. The amplitude spectrum of the Green's function is used to calculate average attenuation between the two stations. Using synthetic seismograms contaminated by noise, it is shown that the Q values calculated from the Green's function are significantly more stable and accurate than those obtained by taking spectral ratios. The method is particularly useful for paths involving short station separations and is applied to a surface wave path crossing the Iranian Plateau.

Comparative study of the 3D tsunami simulations performed with the use of different approaches to the reconstruction of the bottom movement 

2021 ◽  
Author(s):  
Kirill A. Sementsov ◽  
Sergey V. Kolesov ◽  
Anna V. Bolshakova ◽  
Mikhail A. Nosov
Keyword(s):  
Input Data ◽  
Fault Model ◽  
Earthquake Source ◽  
Data Type ◽  
Ocean Bottom ◽  
Source Type ◽  
Finite Fault ◽  
Finite Fault Model ◽  
Type 3

&lt;p&gt;Information on the earthquake source mechanism (Centroid Moment Tensor) becomes publicly available in a few minutes after the earthquake (for example, https://earthquake.usgs.gov/earthquakes or http://geofon.gfz-potsdam.de/eqinfo). Using this information, we can calculate the ocean bottom displacement in the earthquake area [Leonard, 2010; Okada, 1985] and then use this displacement as an input data for hydrodynamic simulation of the tsunami waves. Let us call this type of input data - Type 1. Somewhat later (and sometimes much later), than CMT, more detailed information on the rupture fault structure (Finite Fault Model) becomes available. According to Finite Fault Model, the rupture fault in the earthquake source consists of a certain number of segments characterized by their dip and strike angles. Each segment consists of a finite number of rectangular subfaults, for each of which a displacement vector, an activation time and a rise time are specified. By applying Okada's formulas to each subfault and using the principle of superposition, we can calculate the ocean bottom displacement in the earthquake area and also use it as an input data for tsunami simulations. Let us call this type of input data - Type 2. However, based on the Finite Fault Model, we are able to create a third type of input data (Type 3). To do this, it is necessary to take into account the displacement start time (subfault activation time) and the displacement duration (subfault rise time) of each subfault and consider the dynamics of the rupture process. In this case, we will be able to reconstruct not only the coseismic bottom displacement in the earthquake source (Type 2), but also describe the dynamics of the coseismic bottom displacement formation in the tsunami source (Type 3).&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;This paper compares the tsunami simulation results performed with the of different types of input data (Type 1, Type 2 and Type 3). We performed calculations for a number of large earthquakes at the beginning of the 21st century. We took all the earthquake source information from the USGS catalog (https://earthquake.usgs.gov/earthquakes). The bottom deformations of all three types were calculated using the ffaultdisp code (http://ocean.phys.msu.ru/projects/ffaultdisp/). Tsunami modeling was carried out using a combined 2D / 3D CPTM model [Nosov, Kolesov, 2019; Sementsov et al., 2019]. The simulation results are compared with each other as well as with the DART ocean bottom observatories records.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;The study was supported by Russian Foundation for Basic Research (projects 20-35-70038, 19-05-00351, 20-07-01098).&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

scholarly journals Surface Wave Path Corrections and Source Inversions in Southern California

2010 ◽  
Vol 100 (6) ◽  
pp. 2891-2904 ◽  
Author(s):  
Y. Tan ◽  
A. Song ◽  
S. Wei ◽  
D. Helmberger
Keyword(s):  
Surface Wave ◽  
Southern California ◽  
Wave Path

Kinematic reconstructions of the Western Mediterranean area since Triassic time: possible scenarios and their implications for the Apennines

2020 ◽  
Author(s):  
Eline Le Breton
Keyword(s):  
Tectonic Evolution ◽  
Driving Forces ◽  
Tectonic Setting ◽  
Mediterranean Area ◽  
Magnetic Anomalies ◽  
Western Mediterranean ◽  
Plate Boundaries ◽  
The Past ◽  
The North ◽  
Kinematic Evolution

&lt;p&gt;The Western Mediterranean-Alpine belt is remarkable for its tectonic complexity, i.e. strong arcuation of plate boundaries, fast trench retreat, upper-plate extension and switch of subduction/collision polarity around the Adriatic plate (Adria). The kinematic evolution of the Western Mediterranean area is enigmatic due to the intermittently motion of small continental plates (Adria, Iberia and Sardinia-Corsica) that are caught between two major plates (Africa and Europe), converging since Cretaceous time. Reconstructing the past motion of these micro-plates is challenging due to the strong deformation of their boundaries but is key to understand the geodynamic evolution of the whole area.&lt;/p&gt;&lt;p&gt;The Neogene tectonic evolution is well constrained using magnetic anomalies and transform zones in the Atlantic Ocean for the motion of Europe, Iberia and Africa, and by reconstructing the amount of convergence along fold-and-thrust belts (Apennines, Alps, Dinarides, Provence) and coeval divergence along extensional basins (Liguro-Provencal and Tyrrhenian basins, Sicily Channel Rift Zone) for the motion of Adria and Sardinia-Corsica. Those reconstructions show that Adria had a slight independent motion from Africa and rotated counter-clockwise of about 5&amp;#186; relative to Europe since 20 Ma. However, uncertainties increase and debates arise as one goes back in time. The main debates concern the past motion of Iberia and where its motion relative to Europe is being accommodated in Mesozoic time. Different kinematic scenarios have been proposed depending on the interpretation of paleomagnetic dataset of Iberia, magnetic anomalies in the North Atlantic, and geological-geophysical record of deformation in the Pyrenees and between Iberia and Sardinia-Corsica. Those scenarios have different implications for the tectonic evolution of the Apennines, especially for the Permian-Triassic paleo-tectonic setting of Sardinia, Calabria and Adria, and for the extent and timing of closure of the Liguro-Piemont Ocean. It is important to discuss those implications to better understand subduction processes in the Apennines and their driving forces.&lt;/p&gt;

Seismic strain rate and deep slab deformation in Tonga

1991 ◽  
Vol 96 (B9) ◽  
pp. 14429-14444 ◽  
Author(s):  
Karen M. Fischer ◽  
Thomas H. Jordan
Keyword(s):  
Strain Rate ◽  
Seismic Strain Rate ◽  
Seismic Strain

Retrieving 2D structures from surface-wave data by means of space-varying spatial windowing

Geophysics ◽  
2012 ◽  
Vol 77 (4) ◽  
pp. EN39-EN51 ◽  
Author(s):  
Paolo Bergamo ◽  
Daniele Boiero ◽  
Laura Valentina Socco
Keyword(s):  
Surface Wave ◽  
Real Data ◽  
Processing Technique ◽  
Dispersion Curves ◽  
Data Sets ◽  
Local Dispersion ◽  
Wave Data ◽  
Survey Line ◽  
Wave Path ◽  
Surface Wave Data

Surface-wave techniques are mainly used to retrieve 1D subsurface models. However, in 2D environments, the 1D approach usually neglects the presence of lateral variations and because the surface-wave path crosses different materials, the resulting model is a simplified or misleading description of the site. We tested a processing technique to retrieve 2D structures from surface-wave data acquired with a limited number of receivers. Our technique was based on a two-step process. First, we extracted several local dispersion curves along the survey line using a spatial windowing based on a set of Gaussian windows with different shapes; the window maxima span the survey line so that we were able to extract a dispersion curve from the seismic record for every window. This provided a set of local dispersion curves each of them referring to a different subsurface portion. This space varying spatial windowing provided a good compromise between wavenumber resolution and the lateral resolution of the obtained local dispersion curves. In the second step, we inverted the retrieved set of dispersion curves using a laterally constrained inversion scheme. We applied this procedure to the processing of synthetic and real data sets and the method proved to be successful in reconstructing even complex 2D structures in the subsurface.

The role of the shear mach number in earthquake source dynamics

1976 ◽  
Vol 66 (6) ◽  
pp. 1787-1799
Author(s):  
Ari Ben-Menahem
Keyword(s):  
Mach Number ◽  
Particle Motion ◽  
Surrounding Medium ◽  
Earthquake Source ◽  
Physical Parameters ◽  
Moving Force ◽  
Functional Relations ◽  
Shallow Earthquakes ◽  
Klein Gordon ◽  
The Time Domain

abstract The effect of the rupture velocity upon the spatial and temporal dependence of earthquake source functions is investigated. To this end a model is suggested in which the fault zone is realized as a flexible membrane under the action of a moving force with additional stiffness forces provided by the surrounding medium. The motion of each particle of the membrane is impeded by a displacement-dependent friction and radiation damping. The particle motion along the fault is found to obey an inhomogeneous Klein-Gordon equation whose solutions are derived in closed form. In the time domain, the solutions yield a particle-motion function that has frequently been derived by analysis of earthquake seismograms. The physical parameters in the theoretical source function are found to depend strongly on the Mach number, as already predicted by the theoretical directivity function. The theory excludes the possibility of supersonic rupture and asserts a transonic rupture for major shallow earthquakes and subsonic rupture for seismic events with low and intermediate magnitudes. It predicts new functional relations between the initial particle velocity at the fault's tip, D˙0, the Mach number, M = ν/β, the rise time τ, the stress drop σ∞ and the fault length L.

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