Coseismic displacements and Mw estimation of the El Mayor-Cucapah earthquake, Mexico, from GPS source spectra
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Abstract:
El Mayor-Cucapah earthquake Mw 7.2 on April 4, 2010, occurred on Mexicali Valley near the international border between California, USA and Baja California, Mexico. The objective of this paper was to examine GPS as a complementary tool for seismic studies and to estimate earthquake seismic moment and Mw. For this purpose the capabilities of high-rate GPS (5 Hz) data located in the northern part of the seismic rupture has been explored to obtain the kinematic coseismic displacements. GPS data were processed using Precise Point Positioning method with GIPSY-OASIS II software, then applying the Fast Fourier Transform to the position time series, spectral parameters, seismic moment and Mw were calculated. A good agreement was found in terms of signal correlation of the GPS displacements, by comparing strong-motion seismic records integrated to displacement, using filtering parameters for two sets of instruments. Kinematic GPS displacement spectra clearly shows the low frequency displacement spectral level (~0.2 Hz) when compared with double integration of strong-motion data. It is easy to calculate the static coseismic motion from GPS data, however it is very difficult to calculate it from strong-motion data. A simple earthquake source model is suitable for the GPS dataset used in this work, estimated on Mw=7.19±0.13, was in according with Mw 7.2 obtained in other studies of the El Mayor-Cucapah earthquake.Keywords:
Seismic moment
Precise Point Positioning
Moment magnitude scale
In this study we analyse records from the 'Les Saintes' seismic sequence following the Mw= 6.3 earthquake of 2004 November 11, which occurred close to Guadeloupe (French West Indies). 485 earthquakes with magnitudes from 2 to 6, recorded at distances between 5 and 150 km are used. S-waves Fourier spectra are analysed to simultaneously determine source, path and site terms. The results show that the duration magnitude routinely estimated for the events that occurred in the region underestimate moment magnitude by 0.5 magnitude units over the whole magnitude range. From the inverted seismic moments and corner frequencies, we compute Brune′s stress drops. We show that stress drops increase with increasing magnitude. The same pattern is observed on apparent stresses (i.e. the seismic energy-to-moment ratio). However, the rate of increase diminishes at high magnitudes, which is consistent with a constant stress drop model for large events. Using the results of the inversions, we perform ground motion simulations for the entire data set using the SMSIM stochastic simulation tool. The results show that a good fit (s= 0.25) with observed data is achieved when the source is properly described by its moment magnitude and stress drop, and when site effects are taken into account. Although the magnitude-dependent stress drop model is giving better results than the constant stress drop model, the interevent variability remains high, which could suggest that stress drop depends on other parameters such as the depth of the hypocentre. In any case, the overall variability is of the same order of magnitude as usually observed in empirical ground motion prediction equations.
Moment magnitude scale
Seismic moment
Richter magnitude scale
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Seismic moment
Moment magnitude scale
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Seismic moment
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Summary Intensity is a basic parameter for assessment historical seismicity - realized until the instrumental period. The relation between intensity and seismic moment magnitude allows the creation of a homogeneous catalog. The homogeneous catalog provides compatibility of the input seismological data and allow reliable estimation of the energy distribution of earthquakes - an important stage in seismological research and essential for seismic hazard assessment. In this study are analyzed 92 earthquakes with magnitude above 4.0 (M>4.0), which occurred in space window 37.0° – 45.0° N; 21.0° – 30.0° E, during the time period 1912 – 2018 and the coefficients of the linear regression MW=MW(I0/Imax) are evaluated.
Moment magnitude scale
Seismic moment
Richter magnitude scale
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The December 26, 2004 Sumatra–Andaman Island earthquake, which ruptured the Sunda Trench subduction zone, is one of the three largest earthquakes to occur since global monitoring began in the 1890s. Its seismic moment was M 0 = 1.00 × 1023–1.15 × 1023 Nm, corresponding to a moment-magnitude of M w = 9.3. The rupture propagated from south to north, with the southerly part of fault rupturing at a speed of 2.8 km/s. Rupture propagation appears to have slowed in the northern section, possibly to ∼2.1 km/s, although published estimates have considerable scatter. The average slip is ∼5 m along a shallowly dipping (8°), N31°W striking thrust fault. The majority of slip and moment release appears to have been concentrated in the southern part of the rupture zone, where slip locally exceeded 30 m. Stress loading from this earthquake caused the section of the plate boundary immediately to the south to rupture in a second, somewhat smaller earthquake. This second earthquake occurred on March 28, 2005 and had a moment-magnitude of M w = 8.5.
Moment magnitude scale
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Tsunami earthquake
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