Triggered seismicity in the Andean arc region via static stress variation by the MW = 8.8, February 27, 2010, Maule earthquake

We localized crustal earthquakes in the Andean arc, between 35°S and 36°S, from December 2009 to May 2010. This research shows a seismicity increase, in a narrow longitudinal area, of more than nine times after the great M_w 8.8 Maule earthquake.The localized seismicity defines an area of ∼80 km long and ∼18 km wide and NNW to NNE trend. The M_d magnitudes varied from 0.7 to 3.1 except for two earthquakes with M_w of 3.9 and 4.5, located in the northern end of the area. The focal mechanisms for these two last events were normal/strike-slip and strike-slip respectively.During 2011, a network of 13 temporary stations was installed in the trasarc region in Malargüe, Argentina. Sixty earthquakes were localized in the study region during an 8 month period.We explored how changes in Coulomb conditions associated with the mega-thrust earthquake triggered subsequent upper-plate events in the arc region. We assumed the major proposed structures as receiver faults and used previously published earthquake source parameters and slip distribution for the Maule quake. The largest contribution to static stress change, up to 5 bars, derives from unclamping resulting consistent with co-seismic dilatational deformation inferred from GPS observations in the region and subsidence in nearby volcanoes caused by magma migration.Three different Quaternary tectonic settings–extensional, strike-slip and compressional-have been proposed for the arc region at these latitudes. We found that the unclamping produced by the Maule quake could temporarily change the local regime to normal/strike-slip, or at least it would favor the activation of Quaternary NNE to N-trending dextral strike-slip faults with dextral transtensional movement.     

Assessment of earthquake hazard in Panama based on seismotectonic regionalization

Assessment of seismic hazard in Panama is made using a seismotectonic regionalization model. The coefficients of Gumbel's Type-I distribution are calculated and return periods for several magnitudes are found. From these coefficients intensities, peak ground acceleration and earthquake hazard for a set of return periods and epicentral distances are estimated and substantial variations in the probability of occurrence are noted. The Panama Fracture Zone (PFZ) and the Panama-South America Suture Zone (PSZ) provinces are the most active in producing earthquakes with a magnitude of about 7.0 in less than 16 yr. Magnitude 7.0 earthquakes in the Azuero province have a return period of about 160 yr, whereas in the Panama Deformed Belt (PDB) province the return period for magnitude 7.5 events is about 175 yr.     

Characteristics of the low energy seismicity of central Apulia (southern Italy) and hazard implications

The central part of the Apulia region, in southern Italy, has been generally considered practically free from significant level of seismicity, but historical documentation, geological indicators and recent instrumental observations suggest that the activity of local minor tectonic structures could have been masked (and partly also induced) by that of major seismogenic structures located in the neighbouring regions. A revision of the central Apulia seismicity characteristics was conducted considering its space and time distribution, energy release rate and focal mechanisms, in view of possible hazard implications. To better constrain the seismicity rates inferable from the set of available historical data, special attention was paid to the declustering of a catalogue of low energy events (magnitude < 3.5) instrumentally detected in about 20 years: a new declustering procedure, useful for cases like to the one at hand, was purposely devised taking into account the peculiarity of local seismicity characteristics and the limitations of the available database. The results obtained by combining instrumental and historical data show that this area is affected by a rather sporadic seismicity, likely associated to a general tensional regime and possibly stimulated by the interaction with Apenninic and northern Apulia seismogenic activity. Even though less energetic, the local seismicity contributes to increase the moderately damaging shaking probability due to the activity of seismic sources located in the near areas, so to justify the adoption of at least a minimum level of caution in relation to the local definition of seismic protection measures.     

The seismic activity in Syria and Palestine during the middle of the 8th century; an amalgamation of historical earthquakes

Some historical earthquakes are distinct owing to the geographical distance of the places affected. It is less clear, however, when more than one earthquake is amalgamated into a single event and their combined effects are attributed to a major event. In order to avoid gross overestimation of the size of historical earthquakes the separation and identification of the constituent earthquakes is an important consideration. As an example we show how the tendency of early and modern writers to amalgamate or duplicate earthquakes in Syria and Palestine can lead to the creation of major earthquakes, with serious consequences for the assessment of the seismic hazard in the region.     

Multifractal and Chaotic Analysis of Vrancea (Romania) Intermediate-depth Earthquakes: Investigation of the Temporal Distribution of Events

The Vrancea seismic region contains an isolated cluster of events beneath the Carpathian Arc Bend in Romania, dipping to about 200 km depth. Seismic activity mainly occurs at intermediate depths (h > 60 km). The main goal of the paper is to perform an in-depth, complex analysis of the occurrence times of these intermediate-depth events. We also try to show the versatility of the methods used to characterize different aspects of the seismicity evolution and to offer a user-friendly software toolbox to do most of the related computations. The earthquake catalog used in this study spans from 1974 to 2002 and includes only the intermediate-depth events. In the first part of the paper, we analyze the multifractal characteristics of the temporal distribution of earthquakes. The study reveals two distinct scaling regimes. At small scales we found a clear nonhomogeneous, multifractal pattern, while at large scales the temporal distribution of events shows a monofractal, and close to Poissonian (random), behavior. The multifractal behavior at small scales (minutes-hours) is shown to be clearly an effect of the short aftershock sequences that occurred after some major Vrancea earthquakes. In the second part of the paper we analyze whether our temporal series shows a persistent (or anti-persistent) long-term behavior, by using the Detrended Fluctuation Analysis (DFA) method. The results suggest that the analyzed temporal series of Vrancea earthquakes is a non-correlated process. In part three of the paper we seek to determine whether the dynamics of our earthquake system (described by the occurrence time of Vrancea earthquakes) is deterministically chaotic, deriving from a rather simple evolution law, or whether it is stochastic and is generated by a system that possesses many degrees of freedom. The results suggest that our signal is stochastic (probably does not possess an attractor). The limited time-span of the catalog and the analysis performed in this paper cannot rule out the emergence of an interesting, quasi-deterministic and low-dimensional structure in the case of major Vrancea earthquakes.Acknowledgement One of the authors (BE) is grateful to the Japanese Ministry of Education for providing him a Monbusho scholarship for studying in DPRI, Kyoto University. We thank Z.R. Struzik, M Holschneider, J. Mori and D. Kaplan for their useful comments, and acknowledge the support of the staff of DPRI, Kyoto University and the National Inst. for Earth Physics, Bucharest. We thank the two reviewers, M.B. Geilikman and M. Anghel, for their useful suggestions which improved the quality of this work.     

Demarcation and Scaling of Long-term Seismogenesis

A space-time envelope of minor seismicity related to major shallow earthquakes is identified from observations of the long-term Precursory Scale Increase () phenomenon, which quantifies the three-stage faulting model of seismogenesis. The envelope, which includes the source area of the major earthquake, is here demarcated for 47 earthquakes from four regions, with tectonic regimes ranging from subduction to continental collision and continental transform. The earthquakes range in magnitude from 5.8 to 8.2, and include the 24 most recent mainshocks of magnitude 6.4 and larger in the San Andreas system of California, the Hellenic Arc region of Greece, and the New Zealand region, together with the six most recent mainshocks of magnitude 7.4 and larger in the Pacific Arc region of Japan. Also included are the destructive earthquakes that occurred at Kobe, Japan (1995, magnitude 7.2), Izmit, Turkey (1999, magnitude 7.4), and W.Tottori, Japan (2000, magnitude 7.3). The space (A _P ) in the space-time envelope is optimised with respect to the scale increase, while the time (T _P ) is the interval between the onset of the scale increase and the occurrence of the earthquake. A strong correlation is found between the envelope A _P T _P and the magnitude of the earthquake; hence the conclusion that the set of precursory earthquakes contained in the envelope is intrinsic to the seismogenic process. Yet A _P and T _P are correlated only weakly with each other, suggesting that A _P is affected by differences in statical conditions, such as geological structure and lithology, and T _P by differences in dynamical conditions, such as plate velocity. Among other scaling relations, predictive regressions are found between, on the one hand, the magnitude level of the precursory seismicity, and on the other hand, both T _P and the major earthquake magnitude. Hence the method, as here applied to retrospective analysis, is potentially adaptable to long-range forecasting of the place, time and magnitude of major earthquakes.     

太原ML5.0级地震前后的重力场变化

讨论了2002年9月3日太原ML5.0级地震前后重力场的变化.震前2001年12月～2002年6月重力场表现为上升-下降-上升及平静-活动-平静的活动方式.部分测点点值、测段段差值的趋势性异常在持续相当长时间后,于2002年3月发生转折,6月表现为变化加速,点值和段差值的变化幅值在(30～60)×10-8m·s-2之间,地震发生在加速变化过程中.震后该区的重力异常逐渐恢复.重力变化可能是由该区地壳形变、地壳深部质量迁移和断层蠕动共同作用引起的.