A seismotectonic study of the 1908 Messina earthquake

A major earthquake occurred in the Straits of Messina in Southern Italy on December 28, 1908. The shock became known in literature as the “Messina earthquake”. The present paper deals mainly with a re-interpretation of the source mechanism of this shock using modern interpretation techniques. The following parameters are discussed: Epicentre, hypocentre, origin-time, macroseismic intensity, body and surface wave magnitudes, fault-plane solution, seismic moments derived from body and surface waves, residual displacements and tsunami values.The parameters are compared with the tectonic setting of Southern Italy. As a result of the large magnitude (M = 7) and the 30 km long fault extension of this shock, the Messina earthquake reflects the large scale tectonics of Southern Italy more significantly than any other earthquake from which seismograms exist. The focal mechanism studies show a good agreement between the orientation of the shear-plane of the earthquake and the tectonic features of a fault-line which is known from geological data, the so-called Comiso-Catania-Messina-S. Eufemia fault. The rupture of the shallow earthquake was associated with normal faulting. According to the normal faulting mechanism, the earthquake resulted from tensional forces acting approximately perpendicular to the strike direction of the Straits of Messina.Geodetic measurements which were performed shortly before and after the earthquake indicate an apparent asymmetry in the volumes of uplift and subsidence. It is suggestive that there exists a strong net subsidence of material displaced with the earthquake faulting. The normal faulting mechanism of the Messina earthquake is in tectonic accordance with the uprise of olivine basalt in the volcanism observed at Etna. However, the normal faulting is contrary to the postulation of a subducting oceanic plate giving rise to the Calabrian-Sicilian arc-like feature, as this hypothesis would require mainly a compressional zone in the region of the Straits of Messina.     

The Roer Valley Graben earthquake of 13 April 1992 and its seismotectonic setting

A moderately sized pure, normal dip-slip earthquake occurred in the Roer Valley Graben (RVG) near Roermond, The Netherlands on 13 April 1992 at 1h 20m UTC. This contribution presents an overview of the locations, fault-plane solutions and magnitudes obtained for the mainshock and the aftershocks by the different scientific groups involved in their analysis. The observed maximum intensity of VII is compared with that of other earthquakes in the region to illustrate the relatively low level of damage caused by the mainshock.
Using SH and Lg waves recorded at seven local and regional broadband stations, we determine a seismic moment of 1.4 × 10¹⁷ Nm, a static stress drop of 9.7 MPa and an average displacement of 33 cm over a rupture surface of approximately 11 km².
The seismotectonics of the region extending from the RVG to the city of Liège including the western part of the Rhenish Massif (WRM) and the eastern part of the Brabant Massif (EBM) is analysed based on the Roermond earthquake studies and data collected since 1985 by the Belgian seismic network. The geographical distribution of focal mechanism reveals four different seismotectonic regimes in this area. From stress tensor inversion we find that ₃ coincides with the minimum horizontal stress component in the RVG, the WRM and possibly in the EBM, while in the Liège region ₃ is approximately vertical. The minimum horizontal stress component shows a 30° rotation to the north in the WRM and the Liège region and possibly 50° in the EBM when compared with the minimum horizontal stress component in the RVG.     

The Vrancea earthquake of March 4, 1977 — a multiple seismic event and its seismotectonic implications

A study concerning the multiplicity character of Vrancea earthquake of March 4, 1977 based on records of the Romanian seismic network is presented. Four separate shocks within a 9 s interval were recognized of which three with M = 6.0–6.9. Some explanations regarding the macroseismic intensity are made. Also analysed are the shaking duration, the influence of the Carpathian Mountains on the shape of the isoseismal curves and the focal mechanism for the first two main shocks.     

Simultaneous inversion of the aftershock data of the 1993 Killari earthquake in Peninsular India and its seismotectonic implications

The aftershock sequence of the September 30th, 1993 Killari earthquake in the Latur district of Maharashtra state, India, recorded by 41 temporary seismograph stations are used for estimating 3-D velocity structure in the epicentral area. The local earthquake tomography (LET) method of Thurber (1983) is used. About 1500P and 1200S wave travel-times are inverted. TheP andS wave velocities as well asV _P/V_Sratio vary more rapidly in the vertical as well as in the horizontal directions in the source region compared to the adjacent areas. The main shock hypocentre is located at the junction of a high velocity and a low velocity zone, representing a fault zone at 6–7 km depth. The estimated average errors ofP velocity andV _P/V_Sratio are ±0.07 km/s and ±0.016, respectively. The best resolution ofP and S-wave velocities is obtained in the aftershock zone. The 3-D velocity structure and precise locations of the aftershocks suggest a ‘stationary concept’ of the Killari earthquake sequence.     

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.     

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.     

Spatial variations of fundamental seismotectonic parameters for the earthquake occurrences in the Eastern Mediterranean and Caucasus

Natural Hazards - In this study, a comprehensive statistical analysis was made for different parts of the world. For this purpose, fundamental seismotectonic earthquake parameters such as b-value,...     

Long-term seismotectonic influence on the hydrochemical composition of a spring located at Koryaksky-Volcano, Kamchatka: deduced from aggregated earthquake information

The analysis of earthquake-related signals in hydrochemical time series is still a challenging task. Mostly it is unclear how the geometrical and energetic distribution of earthquakes is influencing variation in the hydrochemical composition of monitoring sites, e.g. located close to volcanoes. Past research showed that linear stress-release models alone are not capable to explain sufficiently observed variation in hydrochemical time series due to earthquake activity. A spring located at the base of Koryaksky Volcano, which has shown hydrochemical variation close to 5, major earthquakes, was chosen to analyse relation patterns between hydrochemical variation and seismicity. A possible mechanism, explaining observed hydrochemical variation, that seismic waves trigger an underground water pumping caused by nucleation of gas bubbles in magma was proposed. Consequences are an increase of discharge, gas content in water and changes in the mixing ratios of waters of different genesis. Based on functions of aggregated earthquake information (E) it is herein shown that seismotectonic-triggered processes have a significant influence on the variation of the hydrochemistry of the spring, lasting longer than two decades. At least seven categories of relation patterns between hydrochemical variation and seismotectonic activity E can be identified. A conducted spectral analysis shows that earthquake activity and hydrochemistry share spikes in frequencies. Results prove that the use of functions of transformed aggregated seismic observations is useful to represent the seismotectonic activity for analysing earthquake-related signals in hydrochemical time series.     

Seismic velocity discontinuities in the crust and uppermost mantle beneath the Kanto district, central Japan, identified from receiver function imaging and repeating earthquake activity

We constructed vertical cross-sections of depth-converted receiver function images to estimate the seismic velocity structure of the crust and uppermost mantle beneath the Kanto district, central Japan. Repeating earthquake data for the plate boundary were also used to estimate geometries of the subducting Philippine Sea plate and the subducting Pacific plate. As a result, we present images of some major seismic discontinuities. The upper boundary of the Pacific plate dips to the northwest in northern Kanto and to the west–southwest in southern Kanto with some undulations. On the other hand, the upper boundary of the Philippine Sea plate as a whole dips to the northwest. However, it is concave to the northeast in the southern Boso peninsula. We suggest that the low-velocity mantle wedge may be indicated on the top of both subducting plates. Plate thickness gradually decreases to the northeast. The northeastern end of the Philippine Sea plate is interpreted to be at depths of 45–90 km. The Moho discontinuity in the overriding plate is deeper than 25 km in the northern Kanto. It contacts the subducting Philippine Sea plate in the southwestern part near 35.8°N.     

August 08, 2010, Sheikhupura, Pakistan earthquake: seismotectonic investigation using focal mechanism solution and gravity data

A shallow-focus (3.8?km deep) and low-magnitude (M _L 3.8) earthquake occurred near Sheikhupura on August 08, 2010. Shaking was felt in parts of Potwar and northern Punjab but no associated damage has been reported. Tectonically, this earthquake occurred to the south of the Salt Range in the Punjab Seismic Zone (PSZ), a shallow-focus, moderate-level seismic zone characterized by steeply dipping strike-slip and extensional faults. The focal mechanism solution, using the seismological data of the United States Geological Survey and local observatory, shows an EW-trending fault plane dipping 710?N similar to the normal faults reported in the area previously. On the basis of the imposition of the stress field on the northward-moving Indian plate and the nature of the FMS of the previous and this earthquake, the Sheikhupura earthquake is considered as one of the intraplate earthquakes occurring frequently in the PSZ. The location of the event on the Bouguer gravity maps coincides with the zone of high gravity anomaly reflecting igneous intrusion(s) or, more likely, structural disturbances (i.e., extensional faulting in the basement).     

Paleomagnetic stratigraphy and biostratigraphy of the Plio-Pleistocene in the Kinki district, Japan

The magnetostratigraphic subdivision of the Plio-Pleistocene series in the Kinki district around Osaka in southwest Japan, based on NRM measurements of volcanic ash beds, is correlated with biostratigraphic and paleoclimatic marker beds as well as past sea level oscillations. At least 10 high sea level stands occurred in the study area between about 1.5 and 0.27 million years ago, all associated with relative warming. A significant change in the composition of flora, from Metasequoia to Fagus dominated assemblages, was observed around the Jaramillo event.     

The 2nd century AD earthquake in central Italy: archaeoseismological data and seismotectonic implications

The 2nd century AD earthquake in central Italy is only known by an epigraph that mentions restorations to a damaged weighing-house at the ancient locality of Pagus Interpromium. The available seismic catalogues report this event with the conventional date of 101 AD, a magnitude M _aw of 6.3, and an epicentral location at the village of San Valentino in Abruzzo Citeriore, in the province of Pescara. In order to improve the knowledge of the damage pattern, we gathered all the archaeological data collected during modern excavations at sites located in the area, which were presumably struck by the earthquake. This information is mainly represented by (1) stratigraphic units due to the sudden collapse of buildings over still frequented floors; (2) stratigraphic units demonstrating restoration or re-building of edifices; (3) stratigraphic units formed as the result of the abandonment of sites or of their lack of frequentation for decades or centuries. Only stratigraphic evidence consistent with an earthquake occurrence during the 2nd century AD has been considered. The most recent archaeological material found in a collapsed unit is a coin of Antoninus Pius, dated at 147–148 AD. This may represent a post quem date very close to the occurrence of the earthquake. The gathered information, plus the stratigraphic data that excluded the earthquake occurrence at some sites, has allowed us to roughly delineate an area of possible damage, including the Sulmona Plain and surrounding areas. Comparisons between the possible 2nd century damage distribution and (i) the damage patterns of more recent historical events that have struck the investigated area, (ii) the distribution of virtual intensities obtained by simulating an earthquake having an epicenter in the Sulmona Plain and applying an intensity attenuation relationship and (iii) a shaking scenario obtained by modelling the activation of the major active fault of the Sulmona Plain area (the Mt. Morrone fault) have revealed consistency between the ancient earthquake and the activation of this fault. Since no other historical events can be attributed to this active fault, we conclude that the time that has elapsed since the last fault activation should be in the order of 1,850 years, i.e. a time span that is very close to the recurrence interval of Apennine seismogenic sources. Moreover, considering the fault length, the causative source may be responsible for earthquakes with M up to 6.6–6.7. The comparison between the presumed 2nd century damage and the shaking scenario suggests that the magnitude mentioned is consistent with the presumed effects of the ancient earthquake. Finally, considering that Sulmona (the most important town in the region investigated) is located in the middle of the Mt. Morrone fault hanging wall, we consider it as the probable epicentral area. Therefore, to summarise the information on the 2nd century AD earthquake, we can conclude that (i) it occurred shortly after 147–148 AD; (ii) a magnitude M _w 6.6–6.7 can be attributed to it and (iii) the probable macroseismic epicentral area was Sulmona.     

Carbonaceous material in the Ryoke metamorphic rocks, Kinki district, Japan

Carbonaceous material in the Ryoke pelitic metamorphic rocks in the Wazuka area, Kinki district, Japan, has been studied by X-ray diffraction (XRD) analysis. Detrital graphite in the lower-grade rocks is recognized in both X-ray diffractograms and transmission electron micrographs. Progressive graphitization is considered to have proceeded continuously on the basis of the XRD data of the bulk concentrates of carbonaceous material, and a conspicuous asymmetric shape of XRD peaks in lower-grade samples is ascribed to the mixture of carbonaceous materials with different crystallinities. Fully-ordered graphite does not occur until the highest-grade part of the chlorite-biotite zone. The variation of degree of crystallinity of carbonaceous materials inferred from XRD data is consistent with the prograde mineral zones. The temperatures for the development of fully-ordered graphite are estimated to be between 410° and 440°C in regional metamorphism through comparing the XRD data from low-, medium- and high-pressure types of metamorphic terrains.     

Contact metamorphosed dunite-harzburgite complex in the Chugoku district,western Japan

The Tari-Misaka ultramafic complex, which is emplaced into the Paleozoic sediments and thermally metamorphosed by two younger granitic masses, is divided into four zones on the basis of the mineral assemblage. They are, in order of increasing metamorphic grade: Zone I antigorite-olivine-orthopyroxene-clinopyroxene. Zone II olivine-talc. Zone III olivine-anthophyllite. Zone IV olivine-orthopyroxene. Strongly serpentinized clinopyroxene-bearing harzburgite in Zone I is similar to ordinary Alpine-type harzburgite. In Zonne II, two kinds of olivine are recognized. One is Mg-rich olivine (Fo₉₃ to Fo₉₇) with opaque inclusions and is probably a recrystallization product of serpentine with talc. The other is Fe-rich olivine (Fo₈₈ to Fo₉₃) free of opaque inclusions and is probably a relic of the primary peridotite. Olivine in Zone III and Zone IV is also relatively Mg-rich (Fo₉₁ to Fo₉₅). Chromitite in Zone IV commonly has an assemblage, olivine+cordierite+Mg-Al spinel (Mg/Mg+Fe²⁺, more than 0.9). Enstatite is rare and coexists with less magnesian Mg-Al spinel (Mg/Mg+Fe²⁺, less than 0.9). Petrological and mineralogical characters of the ultramafic rocks can be well explained by thermal metamorphism of strongly serpentinized peridotite by granitic intrusion. Metamorphic zones are consistent with the experimental results in the system MgO-SiO₂-H₂O. The assemblage olivine+cordierite indicates that the metamorphism occurred at relatively low pressures (<3kb).     

Application of a feedforward neural network in the search for Kuroko deposits in the Hokuroku district, Japan

A feedforward neural network with one hidden layer and five neurons was trained to recognize the distance to kuroko mineral deposits. Average amounts per hole of pyrite, sericite, and gypsum plus anhydrite as measured by X-rays in 69 drillholes were used to train the net. Drillholes near and between the Fukazawa, Furutobe, and Shakanai mines were used. The training data were selected carefully to represent well-explored areas where some confidence of the distance to ore was assured. A logarithmic transform was applied to remove the skewness of distance and each variable was scaled and centered by subtracting the median and dividing by the interquartile range. The learning algorithm of annealing plus conjugate gradients was used to minimize the mean squared error of the scaled distance to ore. The trained network then was applied to all of the 152 drillholes that had measured gypsum, sericite, and pyrite. A contour plot of the neural net predicted distance to ore shows fairly wide areas of 1 km or less to ore; each of the known deposit groups is within the 1 km contour. The high and low distances on the margins of the contoured distance plot are in part the result of boundary effects of the contouring algorithm. For example, the short distances to ore predicted west of the Shakanai (Hanaoka) deposits are in basement. However, the short distances to ore predicted northeast of Furotobe, just off the figure, coincide with the location of the Nurukawa kuroko deposit and the Omaki deposit, south of the Shakanai-Hanaoka deposits, seems to be on an extension of short distance to ore contour, but is beyond the 3 km limit from drillholes. Also of interest are some areas only a few kilometers from the Fukazawa and Shakanai groups of deposits that are estimated to be many kilometers from ore, apparently reflecting the network's recognition of the extreme local variability of the geology near some deposits.