Problematic non-double-couple mechanism of the 2002 Amfilochia Mw5 earthquake, Western Greece

Two seismic agencies reported a very low double-couple percentage (DC%) of the Amfilochia earthquake, of about 30% and 60%, by Schweizerischer Erdbebendienst and Mediterranean Very Broadband Seismographic Network, respectively. Near-regional waveforms, carefully analyzed in this paper for the DC%, suggested a higher DC%, ranging from 75 to 100, dependent on the uncertainty of the source position (optimum value DC% = 93). Using a statistical F test, forward modeling of the near-regional data with a single-event low-DC% source yields a significantly worse waveform match. The fit of near-regional data can be further improved (although at the 90% significance level only) when considering a speculative two-event model. The same model, when viewed at the very-low frequency range, reaches the very low DC% values. However, two features make the two-event model unlikely: The two subevents strongly differ in their focal mechanism, and their mutual separation (3.5 s) is larger than the expected duration of this earthquake. Therefore, the two-source model appears to be nothing but an interesting equivalent representation of the non-DC model, providing some insight into the possible origin of the apparently low DC%. Preference is given to the simple interpretation, most clearly supported by the near-regional data, that the Amfilochia earthquake was an almost pure-shear event.     

Waveform inversion and analysis of an unusual earthquake swarm in the Boshan mining area,Shandong Province,China

Moment tensor solutions were retrieved for the earthquake swarm that occurred during November and December 2010 in the Boshan mining area, Shandong Province, China. The results showed that the double-couple components in the source mechanisms were higher at the beginning of the swarm and consisted mainly of shear faulting controlled by tectonic stress. The subsequent events had significant non-double-couple components, indicating tensile faulting. The double-couple components predominately presented as normal faulting and the P axes were orientated almost vertically. The slip vectors of the swarm events were relatively stable. With reference to the tectonic features near the epicenter, we concluded that the swarm was a result of subordinate fault motion related to the Wangmu Mountain fault and that high-pressure pore fluids played a crucial role in the activity of the earthquake swarm.     

Real time test of the long-range aftershock algorithm as a tool for mid-term earthquake prediction in Southern California

Result of the algorithm of earthquake prediction, published in 1982, is examined in this paper. The algorithm is based on the hypothesis of long-range interaction between strong and moderate earthquakes in a region. It has been applied to the prediction of earthquakes withM6.4 in Southern California for the time interval 1932–1979. The retrospective results were as follows: 9 out of 10 strong earthquakes were predicted with average spatial accuracy of 58 km and average delay time (the time interval between a strong earthquake and its best precursor) 9.4 years varying from 0.8 to 27.9 years. During the time interval following the period studied in that publication, namely in 1980–1988, four earthquakes occurred in the region which had a magnitude ofM6.4 at least in one of the catalogs: Caltech or NOAA. Three earthquakes—Coalinga of May, 1983, Chalfant Valley of July, 1985 and Superstition Hills of November, 1987—were successfully predicted by the published algorithm.The missed event is a couple of two Mammoth Lake earthquakes of May, 1980 which we consider as one event due to their time-space closeness. This event occurred near the northern boundary of the region, and it also would have been predicted if we had moved the northern boundary from 38°N to the 39°N; the precision of the prediction in this case would be 30 km.The average area declared by the algorithm as the area of increased probability of strong earthquake, e.g., the area within 111-km distance of all long-range aftershocks currently present on the map of the region during 1980–1988 is equal to 47% of the total area of the region if the latter is measured in accordance with the density distribution of earthquakes in California, approximated by the catalog of earthquakes withM5. In geometrical terms it is approximately equal to 17% of the total area.Thus the result of the real time test shows a 1.6 times increase of the occurrence ofC-events in the alarmed area relative to the normal rate of seismicity. Due to the small size of the sample, it is of course, beyond the statistically significant value. We adjust the parameters of the algorithm in accordance with the new material and publish them here for further real-time testing.     

用P波初动资料确定地震震源机制教程(一)

简要叙述运用P波初动资料确定地震震源机制(断层面解)的原理与方法,并以图解法为例,详细阐述相关的物理概念及求地震震源机制解的具体步骤,以适应具有不同专业背景(例如:地震学、地球物理学、地质学、大地测量学、工程地震学、灾害科学、管理科学)的不同读者(例如:学生、教师、管理人员)的不同需求(例如:了解、学习、应用).