Aleš Špičák

ALP 2002 seismic experiment

The ALP 2002 was organized as an international seismic experiment whose scientific objective is to further scientific understanding of the structure and evolution of the lithosphere in the Eastern Alps and surrounding areas. The ALP 2002 experiment included passive seismic monitoring and an active source seismic refraction experiment. Furthermore, local high-density deployments were carried out in Austria and Hungary to investigate local geologic problems. All data will be integrated with the goal of better understanding the geodynamic processes currently at work and the complex tectonic history of this region.

Magma Intrusions and Earthquake Swarm Occurrence in the Western Part of the Bohemian Massif

We are proposing a hypothesis that earthquake swarms in the West Bohemia/Vogtland seismoactive region are generated by magmatic activity currently transported to the upper crustal layers. We assume that the injection of magma and/or related fluids and gases causes hydraulic fracturing which is manifested as an earthquake swarm at the surface. Our statements are supported by three spheres of evidence coming from the western part of the Bohemian Massif: characteristic manifestations of recent geodynamic activity, the information from the neighbouring KTB deep drilling project and from the 9HR seismic reflection profile, and the detailed analysis of local seismological data. (1) Recent manifestations of geodynamic activity include Quaternary volcanism, rich CO2emissions, anomalies of mantle-derived3He, mineral springs, moffets, etc. (2) The fluid injection experiment in the neighbouring KTB deep borehole at a depth of 9 km induced hundreds of micro-earthquakes. This indicates that the Earths crust is near frictional failure in the western part of the Bohemian Massif and an addition of a small amount of energy to the tectonic stress is enough to induce an earthquake. Some pronounced reflections in the closely passing 9HR seismic reflection profile are interpreted as being caused by recent magmatic sills in the crust. (3) The local broadband seismological network WEBNET provides high quality data that enable precise localization of seismic events. The events of the January 1997 earthquake swarm are confined to an extremely narrow volume at depths of about 9 km. Their seismograms display pronounced reflections of P- and S-waves in the upper crust. The analysis of the process of faulting has disclosed a considerable variability of the source mechanism during the swarm.We conclude that the mechanism of intraplate earthquake swarms generated by magma intrusions is similar to that of induced seismicity. As the recent tectonic processes and manifestations of geodynamic activity are similar in European areas with repeated earthquake swarm occurrence (Bohemian Massif, French Massif Central, Rhine Graben), we assume that magma intrusions and related fluid and gas release at depths of about 10 km are the universal cause of intraplate earthquake swarm generation

Earthquake Swarms and Accompanying Phenomena in Intraplate Regions: A Review

The western part of the Bohemian Massif has played an exceptional role in recent geodynamic activity of the region. It is characterised by repeated occurrences of earthquake swarms and by other manifestations of deep tectonic processes (CO2emissions, anomalous3He content, mineral waters, mofettes, etc.). The purpose of this paper is to introduce some other intraplate regions with earthquake swarm occurrence (French Massif Central; Colli Albani and Vulsini Mts., central Italy; Southern Apennines, Italy; the Danville and Long Valley regions, California; central Arkansas), and with artificially induced earthquake swarms (Larderello, Italy, geothermal field; Coso, California, geothermal field; NE Bavaria, Germany, deep drilling project). Although these areas represent different tectonic environments, the manifestations of recent geodynamic and/or man-made activity are similar in many aspects. This coincidence most probably issues from a common cause of both tectonic and artificially induced earthquake swarms – intrusions/injections of fluids. Since the regions with earthquake swarm occurrence of tectonic origin are situated as a rule in the close neighbourhood of Quaternary volcanoes, the intruding fluids seem to be derived from magma recently transported to upper crustal layers.

Seismically active fracture zones and distribution of large accumulations of metals in the central part of Andean South America

Abstract The analysis of the geometry of distribution of earthquake foci in the central part of Andean South America between 18° and 34°S made the delineation of several seismically active fracture zones in the continental wedge overlying the subducting Nazca plate possible. Correlation of their position with the distribution of hypogene accumulations of metals revealed that the majority of large mineral deposits and mining districts are situated in the outcrops of these fracture zones. We present geometrical documentation (map of epicentres, vertical and longitudinal cross sections) of the most important fracture zones and data on mineralogical composition, genetic type and available radiometric ages of mineral deposits. Sixteen mining districts in Chile, and 24 in Argentina, were attributed to the seismically active fracture zones. Major mining districts and individual large mineral deposits occur in six seismically active fracture zones roughly parallel to the axis of the Peru-Chile trench (Carachas-Portillo, Choquelimpie, Iquique, Domeyko, Río Blanco-Los Bayos and Farellones F.Z.), in six fracture zones roughly perpendicular to the trench (El Salvador, Maricunga, Jaroma, Ujina, Tumbaya and Incahuasi-León Muerto F.Z.) and in two fracture zones oriented at an angle of about 45° in relation to the direction of the presently active Andean subduction (Aconcagua and Sierra del Volcán F.Z.). The occurrences of large mineral deposits of different ages show that these fracture zones were also active in the geological past and represent sites of permanent re-opening of paths allowing ore-bearing solutions and long-term accumulation of large amounts of metals to occur in relatively restricted domains of the Earths crust. The mining districts with dated mineral deposits are arranged into four periods of hypogene mineralization: Upper Miocene-Pliocene, Upper Oligocene-Middle Miocene, Upper Eocene-Middle Oligocene, Lower Paleocene-Upper Eocene. These periods of metallogenic activity correlate well with four supposed Andean subduction cycles active in the Tertiary. The occurrence of mineral deposits of different ages in recently active fracture zones can be used as an important evidence in favour of long-term spatial permanence and activity of these zones and as a guide for the discovery of further mineral deposits hidden under young sedimentary and volcanic cover in the fracture zones.

Seismic Activity Around and Under Krakatau Volcano, Sunda Arc: Constraints to the Source Region of Island Arc Volcanics

There is general agreement that calc-alkaline volcanic rocks at convergent plate margins are genetically related to the process of subduction (Ringwood, 1974; Maaloe and Petersen, 1981; Hawkesworth et al., 1997). However, opinions on the mode and site of generation of primary magma for island arc volcanism differ substantially. The site of generation of calc-alkaline magma is thought to be either in the mantle wedge (Plank and Langmuir, 1988; McCulloch and Gamble, 1991) or in the subducting slab (White and Dupré, 1986; Defant and Drummond, 1990; Edwards et al., 1993; Ryan and Langmuir, 1993). We present seismological evidence in favour of the latter concept. A distinctive seismicity pattern around and under the Krakatau volcano was identified during systematic studies of the SE Asian convergent plate margins by means of global seismological data. A column-like cluster of events, probably associated with the dynamics of the volcano, is clearly separated from the events in the Wadati-Benioff zone. The accuracy of hypocentral determinations of the events of the cluster does not differ from the accuracy of the events belonging to the subducting slab. The depths of the cluster events vary from very shallow to about 100 km without any apparent discontinuity. On the other hand, there is a pronounced aseismic gap in the Wadati-Benioff zone directly beneath the volcano at depths between 100-150 km. The Krakatau cluster connects this aseismic gap to the volcano at the surface. The pervasive occurrence of earthquakes in the continental wedge between the subducting slab and the Earth surface bears witness to the brittle character of the continental lithosphere and casts doubt on the existence of large-scale melting of mantle material. The aseismic gap (Hanuš and Vaněk, 1985), interpreted by us as a partially melted domain occurring in subducted slabs in practically all active subduction zones that reach depths greater than 100 km, is here used as evidence for the location of the primary source region of island arc volcanics in the subducting plate.

Remarks on seismic energy release related to strike slip and tensile crack mechanisms

РезюмеОсвобож¶rt;енuе сеŭсмuческоŭ энерuu в фuзuческuх мо¶rt;ельях nо¶rt; ¶rt;aвленuе м во время бысmроŭ с¶rt;вuовоŭ uлu оmрывноŭ nо¶rt;вuжкu uзучено nuезоэлекmрuческuм меmо¶rt;ом. В сmamье nре¶rt;ложены хaрaкmерuсmuкu нanрaвленносmu uзлученных волн; оnре¶rt;елены mочкu нaчaлa сеŭсмоaкmuвноŭ с¶rt;вuовоŭ nо¶rt;вuжкu с целю лучщео nоняmuя мехaнuзмa освобож¶rt;енuя сеŭсмuческоŭ энерuu в очaе землеmрясенuя эmоо muna.

Migration of Events During The January 1997 Earthquake Swarm (The West Bohemia/Vogtland Region)

A detailed analysis of the time-space pattern of seismic activity during the January 1997 swarm demonstrates the gradual and ordered migration of earthquake foci, suggesting a step-by-step penetration of crustal fluids into a remarkably small fractured volume.

Position of the Disastrous 1999 Puebla Earthquake in the Seismotectonic Pattern of Mexico

The location of the 1999 Puebla earthquake shows that this earthquake belongs to the class of disastrous intraplate earthquakes generated by fracturing of the continental lithosphere caused by the process of subduction. This is obvious from the vertical section across the Middle American Wadati-Benioff zone and from its position in the revised seismically active Los Azufres-Rio Salado fracture zone delineated in the continental lithosphere of the North American plate.

Wave propagation in physical models of micromorphic media

РезюмеРaсnросmрaненuе сеŭсмuческuх волн в мuкроморфноŭ сре¶rt;е, nо mеорuu о¶rt;ноŭ uз возможных мо¶rt;елеŭ сре¶rt;ы в очaге землеmрясенuя, uзучaеmся nуmём ¶rt;вухмерного ульmрaзвукового мо¶rt;елuровaнuя. Полученные резульmamы nокaзывaюm, чmо maкaя сре¶rt;a оmлuчеamся яркоŭ уnругоŭ aнuзоmроnuеŭ u nовыщенным nоглощенuе⇐. Скоросmь рaсnросmрaненuя nрохо¶rt;ящuх nро¶rt;ольных волн nонuжaеmся, uх aмnлumу¶rt;ы резко меняюmся. Преовлa¶rt;aющaя чaсmоma волн, nрохо¶rt;ящuх мuкроморфноŭ сре¶rt;оŭ, nлaвно сmремumся к о¶rt;ноŭ велuчuне, коmорaя связaнa с nросmрaнсmвенным рaсnре¶rt;еленuем, нanрaвленносmью u рaзмерaмu ¶rt;ефекmов, оnре¶rt;еляющuх эmу сре¶rt;у. Полученые резульmamы срaвнuвaюmся с mеорuеŭ мuкроморфноŭ сре¶rt;ы.SummaryThe propagation of seismic waves in a micromorphic body, which is supposed to be one of the possible models of the medium in the earthquake focus, is studied by means of the two-dimensional ultrasonic model technique. The results obtained indicate that such a medium is characterized by distinct elastic anisotropy and by increased attenuation. The propagation velocity of longitudinal waves decreases and their amplitudes change considerably. The prevailing frequency of the waves passing through the micromorphic medium tends smoothly to one value which depends on the space distribution, orientation and dimensions of the elements characterizing such a medium. The obtained results are confronted with the theory of a micromorphic medium.

Kamchatka subduction zone, May 2013: the Mw 8.3 deep earthquake, preceding shallow swarm and numerous deep aftershocks

A sequence of 98 teleseismically recorded earthquakes occurred off the east coast of Kamchatka at depths between 10-90 km around latitude 52.5°N and longitude 160°E on May 16–23, 2013. The swarm occurred along the northern limit of the rupture area of the 1952 Mw 9.0 great Kamchatka earthquake, the fifth largest earthquake in the history of seismic observations. On May 24, 2013 the strongest deep earthquake ever recorded of Mw 8.3 occurred beneath the Sea of Okhotsk at a depth of 610 km in the Pacific slab of the Kamchatka subduction zone, becoming the northernmost deep earthquake in the region. The deep Mw 8.3 earthquake occurred down-dip of the shallow swarm in a transition zone between the southern deep and northern shallow segments of the Pacific slab. Several deep aftershocks followed, covering a large, laterally elongated part of the slab. We suppose that the two described earthquake sequences, the May 16–23 shallow earthquake swarm and the May 24–28 deep mainshock-aftershock series, represent a single tectonic event in the Pacific slab having distinct properties at different depth levels. A low-angle underthrusting of the shallow part of the slab recorded by the shallow earthquake swarm activated the deep part; this process induced the deep mainshock-aftershock series only three days after the swarm. The domain of the subducting slab activated by the May 2013 earthquake occurrence was extraordinarily large both down-dip and along-strike.