Magnitude Scaling of Early-Warning Parameters for the Mw 7.8 Tocopilla, Chile, Earthquake and Its Aftershocks
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We studied the correlation between the final event magnitude and four parameters obtained from the early portion of P and S phases for a set of high quality subduction events.These relationships are used in the framework of earthquake earlywarning systems for real-time magnitude estimation.The investigated parameters are the low-pass-filtered peak displacement (PD), the integral of the velocity squared (IV2), and the predominant and characteristic periods (τ p and τ c ).We created a dataset from the continuous records of the first two weeks following the 14 November 2007 M w 7.8 Tocopilla (Chile) earthquake.The dataset includes 69 events with magnitudes greater than 4, among them the main event (M w 7.8), the main aftershocks of M w 6.7 occurred on November 15, and 4 events with magnitude greater than 6.The low-pass-filtered PD read on short P-phase and S-phase windows is well correlated with the final magnitude, confirming previous results.Indeed when examining 2-s time windows of P waves, we did not observe any saturation effect for magnitudes greater than 6.5; however, there is a slope change in the regression curve.A similar result is obtained from the integral of squared velocity computed over short windows around P and S waves.The characteristic and predominant periods are correlated with magnitudes up to M w 6; but they clearly do not scale with the magnitude for the stronger events.Our observations offer insight into the feasibility of an early-warning system in Chile.Keywords:
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Abstract On September 12, 1966, at 16h 41m, an earthquake of magnitude 6.0 to 6.5 occurred about 10 km northeast of Truckee, California. Hypocenters of 158 after-shocks that occurred between September 14 and 25 were found to be within a volume 3 km wide by 10 km long by 12 km deep. The magnitude-frequency curve appears anomalous, as there seem to be too many shocks greater than magnitude 2 compared to the number of small ones under magnitude 0.5. Nodal-plane determinations indicate two modes of faulting for the aftershocks. Strike-slip faulting with nodal planes striking N. 40°W. and N. 50°E. is dominant; secondary normal faulting occurs on nodal planes striking nearly north. An attempt is made to relate the strain release pattern of these aftershocks to major regional right-lateral shear and extension.
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The Firuzabad (Iran) earthquake of the 16th August 1958 had a smaller magnitude (il/ = 6.6) than did the last major earthquake in the same area which occurred on the 13th December 1957, and had a 7.1 magnitude. The Firuzabad earthquake killed 132 and injured about 200 people in 170 villages. It affected an area of 1,100 square kilometres -within which 2,500 housing units were destroyed or damaged beyond repair. The earthquake had its macroseismic epicentre somewhat southeast of the 1957 earthquake and the shock was felt over an area of 80,000 square kilometres. The damage pattern from the Firuzabad earthquake did not resemble that of the 1957 shock, in that the Firuzabad earthquake affected a smaller region but was the more intense of the two. In contrast, the 1957 earthquake had a somewhat more moderate surface intensity over a much wider area. The Firuzabad earthquake was associated with a fault-zone at least 20 kilometres long. This earthquake and the seismic events of the previous year as well as the aftershocks of the 21st of September 1958, show quite clearly a progressive expansion of seismic activity along a northwest-southwest axis in the Zagros mountains.
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Abstract The 19 October, 1985 Ardsley, New York magnitude 4.0 mainshock can be characterized as the superposition of three sub-events. Aftershocks of the 31 March, 1982 Miramichi, New Brunswick magnitude 5.0 earthquake occur at nearly the same depth as the mainshock, approximately 3 km, and at least one aftershock is resolvably deeper by several kilometers. These results are interpreted from observations of digital recordings of near-regional seismograms.
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Abstract Data derived from studies by other workers of prominent, well-defined aftershock sequences are employed to obtain evidence for the source dimensions of earthquakes in the magnitude range m = 4 1 2 to 6. The characteristic length of the aftershock zone is defined as the longest dimension of the map view of the aftershock epicenters. On the basis of this aftershock data, the following rough limits may be placed on the likely size of small earthquakes in the western United States: for magnitude 5 events, 5 to 25 km; for magnitude 4 events, 2 to 15 km. These limits are about an order of magnitude larger than those proposed by Press for earthquakes and underground explosions and represent an independent confirmation of the results for earthquakes of Wyss and Brune. These results have an important bearing on recent studies of the excitation of surface waves by earthquakes and underground explosions.
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Abstract The earthquakes in Turkey (Kahramanmaraş province) in February 2023 do not fit into the usual mainshock–aftershocks sequence. According to Bath’s statistical law [1], the magnitude of the strongest aftershock is expected to be one less than the magnitude of the mainshock. Meanwhile, for the aftershock sequence in Turkey, the difference in magnitude is only 0.1. In Turkish publications, the first of the strongest earthquakes is called Pazardzhik ( M w = 7.8) and the second, Elbistan ( M w = 7.7). Each of these earthquakes generated its own system of surface ruptures and aftershock sequences differently oriented in space. The purpose of this study is to assess whether the occurrence of the second earthquake is due to a stress field that existed earlier or if it arose as a result of the mainshock. If the second scenario was realized, the stress field can be almost instantly changed in the vicinity of a strong earthquake (the time difference between the earthquakes was less than nine hours).
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