Determination of regional earthquake parameters from surface wave records

We consider in this paper the possibility of the source models construction for two regional earthquakes: in Akaba (June 27, 2015, Mw=5.5) and in the Dead Sea region (July 4, 2018, Mw=4.8) by surface wave records analysis. Fundamental Love and Rayleigh modes recorded by seismic networks IRIS, GEOSCOPE, and GEOFON were used for this purpose. At the first stage, at zero approximation we describe the source by moment tensor, considering the instantaneous point shear dislocation (double-couple) at a given depth. Four equivalent solutions were obtained from the amplitude spectra of surface waves. For an unambiguous choice of a solution, additional data were used, such as the signs of the first P-wave arrivals (for the Aqaba earthquake) or phase spectra (for an earthquake in the Dead Sea) were calculated for each of the four solutions. Based on the minimum values of the constructed joint residuals, a unique solution was chosen for each event. Then, considering the source flat, the following integral parameters were obtained: the duration of the process in the source, the lengths of the major and minor axes of the source, the average instant centroid velocity, the angle between the major axis of the source and the axis of the strike, the angle between the direction of motion of the instant centroid and the axis of the strike. The quality of the obtained solutions is estimated using the normalized residual function. This function characterizes the difference between the theoretical amplitude spectra and the observed ones. In the case of the earth-quake in the Dead Sea, the resolution of this function for some parameters was so small that it was not possible to obtain a solution. Also, for the earthquakes under consideration, the ambiguity associated with a significant excess of the surface wavelengths over the depth of the shallow source was analyzed

Download Full-text

Effects of centroid location on determination of earthquake mechanisms using long-period surface waves

Bulletin of the Seismological Society of America ◽

10.1785/bssa0800051205 ◽

1990 ◽

Vol 80 (5) ◽

pp. 1205-1231

Author(s):

Jiajun Zhang ◽

Thorne Lay

Keyword(s):

Surface Wave ◽

Rayleigh Waves ◽

Body Wave ◽

Moment Tensor ◽

Source Location ◽

P Wave ◽

Nodal Plane ◽

Wave Source ◽

Long Period

Abstract Determination of shallow earthquake source mechanisms by inversion of long-period (150 to 300 sec) Rayleigh waves requires epicentral locations with greater accuracy than that provided by routine source locations of the National Earthquake Information Center (NEIC) and International Seismological Centre (ISC). The effects of epicentral mislocation on such inversions are examined using synthetic calculations as well as actual data for three large Mexican earthquakes. For Rayleigh waves of 150-sec period, an epicentral mislocation of 30 km introduces observed source spectra phase errors of 0.6 radian for stations at opposing azimuths along the source mislocation vector. This is larger than the 0.5-radian azimuthal variation of the phase spectra at the same period for a thrust fault with 15° dip and 24-km depth. The typical landward mislocation of routinely determined epicenters of shallow subduction zone earthquakes causes source moment tensor inversions of long-period Rayleigh waves to predict larger fault dip than indicated by teleseismic P-wave first-motion data. For dip-slip earthquakes, inversions of long-period Rayleigh waves that use an erroneous source location in the down-dip or along-strike directions of a nodal plane, overestimate the strike, dip, and slip of that nodal plane. Inversions of strike-slip earthquakes that utilize an erroneous location along the strike of a nodal plane overestimate the slip of that nodal plane, causing the second nodal plane to dip incorrectly in the direction opposite to the mislocation vector. The effects of epicentral mislocation for earthquakes with 45° dip-slip fault mechanisms are more severe than for events with other fault mechanisms. Existing earth model propagation corrections do not appear to be sufficiently accurate to routinely determine the optimal surface-wave source location without constraints from body-wave information, unless extensive direct path (R1) data are available or empirical path calibrations are performed. However, independent surface-wave and body-wave solutions can be remarkably consistent when the effects of epicentral mislocation are accounted for. This will allow simultaneous unconstrained body-wave and surface-wave inversions to be performed despite the well known difficulties of extracting the complete moment tensor of shallow sources from fundamental modes.

Download Full-text

Estimating Sinkhole Hazard in the Dead Sea Coastal Area Using P-wave Velocities and Magnetic Resonance Soundings

Near Surface 2008 - 14th EAGE European Meeting of Environmental and Engineering Geophysics ◽

10.3997/2214-4609.20146304 ◽

2008 ◽

Cited By ~ 1

Author(s):

A. Legchenko ◽

M. Ezersky ◽

M. Boucher ◽

C. Camerlynck ◽

A. Al-Zoubi ◽

...

Keyword(s):

Magnetic Resonance ◽

Coastal Area ◽

Dead Sea ◽

P Wave ◽

Wave Velocities ◽

The Dead ◽

P Wave Velocities ◽

Sinkhole Hazard

Download Full-text

Reliability tests of moment tensor inversion of anthropogenic seismicity

10.5194/egusphere-egu21-12859 ◽

2021 ◽

Author(s):

Anna Tymińska ◽

Grzegorz Lizurek

Keyword(s):

Moment Tensor ◽

P Wave ◽

Quality Data ◽

Seismic Moment Tensor ◽

Signal Ratio ◽

Amplitude Inversion ◽

Double Couple ◽

Anthropogenic Seismicity ◽

Determine Mechanism ◽

Seismic Networks

<p>Seismic moment tensor becomes part of basic seismic data processing. For anthropogenic events mostly common and available method to determine mechanism is amplitude inversion. However essential for correct amplitude inversion are good quality data. Factors commonly occurring in anthropogenic seismicity like high noise to signal ratio, low magnitude and shortage of seismic stations with unfavorable focal coverage can introduce undetected errors to inversion solution. In this work, synthetic tests for two seismic networks are presented to examine the reliability of P-wave first peak amplitude inversion for these areas. The synthetic tests of the noise influence on the results of full MT solutions were carried out for two surface networks monitoring anthropogenic seismicity: VERIS network in Vietnam and LUMINEOS network in Poland. Various mechanisms with double couple component variability from 10% to 100% were considered to take into account mechanisms caused by different types of human activity. High variability of solutions in tests shows that some spurious components cannot be avoided in full moment tensor solutions obtained for presented networks in certain cases.</p><p>This work was partially supported by research project no. 2017/27/B/ST10/01267, funded by the National Science Centre, Poland, under agreement no. UMO-2017/27/B/ST10/01267.</p>

Download Full-text