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We report on more than 100 earthquake waveform doublets in five subduction zones, including an earthquake nest in Bucaramanga, Colombia. Each doublet is presumed to be a pair of earthquakes that repeat at essentially the same location. These doublets are important for studying earthquake physics, as well as temporal changes of the inner core. Particularly, our observation from one South Sandwich Islands (SSI) doublet recorded at station INK in Canada shows an inner core traveltime change of ∼0.1 s over ∼6 yr, confirming the inner-core differential motion occurring beneath Central America. Observations from one Aleutian Islands doublet, recorded at station BOSA in South Africa, and from one Kuril Islands doublet, recorded at station BDFB in Brazil, show an apparent inner core traveltime change of ∼0.1 s over ∼7 yr and ∼6 yr, respectively, providing evidence for the temporal change of inner core properties beneath Central Asia and Canada, respectively. On the other hand, observations from one Tonga–Fiji–Solomon Islands doublet, recorded at station PTGA in Brazil, and from one Bucaramanga doublet, recorded at station WRAB in Australia and station CHTO in Thailand, show no/little temporal change (no more than 0.005 s yr−1 , if any) of inner core traveltimes for the three corresponding ray paths for which the path in the inner core is nearly parallel to the equatorial plane. Such a pattern of observations showing both presence and possible absence of inner-core traveltime change can be explained by the geometry and relative directions of ray path, lateral velocity gradient and inner-core particle motion due to an eastward super-rotation of a few tenths of a degree per year. 相似文献
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M. Mesimeri V. Karakostas E. Papadimitriou D. Schaff G. Tsaklidis 《Journal of Seismology》2016,20(2):595-614
The 2013 Aigion earthquake swarm that took place in the west part of Corinth Gulf is investigated for revealing faulting and seismicity properties of the activated area. The activity started on May 21 and was appreciably intense in the next 3 months. The recordings of the Hellenic Unified Seismological Network (HUSN), which is adequately dense around the affected area, were used to accurately locate 1501 events. The double difference (hypoDD) technique was employed for the manually picked P and S phases along with differential times derived from waveform cross-correlation for improving location accuracy. The activated area with dimensions 6?×?2 km is located approximately 5 km SE of Aigion. Focal mechanisms of 77 events with M?≥?2.0 were determined from P wave first motions and used for the geometry identification of the ruptured segments. Spatio-temporal distribution of earthquakes revealed an eastward and westward hypocentral migration from the starting point suggesting the division of the seismic swarm into four major clusters. The hypocentral migration was corroborated by the Coulomb stress change calculation, indicating that four fault segments involved in the rupture process successively failed by stress change encouragement. Examination of fluid flow brought out that it cannot be unambiguously considered as the driving mechanism for the successive failures. 相似文献
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The Applicability of Modern Methods of Earthquake Location 总被引：7，自引：0，他引：7
Paul G. Richards Felix Waldhauser David Schaff Won-Young Kim 《Pure and Applied Geophysics》2006,163(2-3):351-372
We compare traditional methods of seismic event location, based on phase pick data and analysis of events one-at-a-time, with
a modern method based on cross-correlation measurements and joint analysis of numerous events. In application to four different
regions representing different types of seismicity and monitored with networks of different station density, we present preliminary
results indicating what fraction of seismic events may be amenable to analysis with modern methods. The latter can supply
locations ten to a hundred times more precise than traditional methods. Since good locations of seismic sources are needed
as the starting point for so many user communities, and potentially can be provided due to current improvements in easily-accessible
computational capability, we advocate wide-scale application of modern methods in the routine production of bulletins of seismicity.
This effort requires access to waveform archives from well-calibrated stations that have long operated at the same location. 相似文献
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