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UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-23 17:43 |
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Conference: Bucharest University Faculty of Physics 2009 Meeting
Section: Atmosphere and Earth Science; Environment Protection
Title:
Significant earthquakes, with different focal mechanisms, accompanied by correspondingly contrasting signatures of subsurface temperatures: Na-K-Mg geothermometry diagnoses in Romania (Vrancea area) and in northern Italy
Authors:
H. Mitrofan (1), F. Chitea (1,2), M.-A. Anghelache (1), C. Marin (3), A. Tudorache (3)
Affiliation:
(1) Institute of Geodynamics of the Romanian Academy, Bucharest, Romania (florina_chitea@geodin.ro)
(2) University of Bucharest, Romania
(3) Institute of Speleology of the Romanian Academy, Bucharest, Romania
E-mail
f_chitea@yahoo.com
Keywords:
Na-K-Mg geothermometry, earthquakes, groundwater, monitoring
Abstract:
By using ionic (Na, K, Mg) geothermometry, anomalous fluctuations of subsurface temperatures have been previously detected on occurrence of several significant (M>5) earthquakes recorded worldwide (Egypt, India, Romania). In all those cases, the ionic composition of certain groundwater discharges had been noticed to display just one significant fluctuation episode, in correspondence to one important seismic event.In contrast, the present investigation addresses monitoring operations which have been, each one, influenced by two important (Mb≥5) earthquakes, whose focal mechanisms were, moreover, significantly different from one another. Specifically, we have processed, by means of the Na-K-Mg geothermometry approach, data collected during monitoring operations conducted next to Vrancea area, Romania (between 1997-1999), and in northern Italy (between 2004-2005).
In Vrancea region, both major earthquakes of that period occurred at intermediate depths (150 km) and displayed a reverse-faulting mechanism; yet, while the P-axis of the first event displayed a habitual, NW-SE strike, the P-axis of the second event exhibited a less usual, SW-NE strike. Correspondingly, the Na-K-Mg geothermometry analysis indicated dissimilar patterns for the subsurface temperature evolutions associated to each of the two seismic events.In northern Italy, within a 3 radius around the monitored spring, two significant events occurred, both of them at shallow (10 km) depth. For both events, focal mechanisms indicated NW-SE compression, yet the T-axis changed from near-horizontal, for the first event, to near-vertical, for the second one. Accordingly, a pattern of increased subsurface temperatures was recorded in the first case, while the opposite pattern (decreased subsurface temperatures) was noticed on occurrence of the second event. One possible explanation was that horizontal tension favoured deeper cracks opening and associated intrusions of hotter water, from larger depths. The above-mentioned associations with specific temperature signatures suggest that the seismogenesis-related processes concerned quite extensive regions, within which long-range lithospheric interactions operated.
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