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| Titel |
Near-seismic effects in ULF fields and seismo-acoustic emission: statistics and explanation |
| VerfasserIn |
O. Molchanov, A. Schekotov, M. Solovieva, E. Fedorov, V. Gladyshev, E. Gordeev, V. Chebrov, D. Saltykov, V. I. Sinitsin, K. Hattori, M. Hayakawa |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1561-8633
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| Digitales Dokument |
URL |
| Erschienen |
In: Natural Hazards and Earth System Science ; 5, no. 1 ; Nr. 5, no. 1 (2005-01-03), S.1-10 |
| Datensatznummer |
250002185
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| Publikation (Nr.) |
 copernicus.org/nhess-5-1-2005.pdf |
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| Zusammenfassung |
| Preseismic intensification of fracturing has been investigated from
occurrence analysis of seismo-acoustic pulses (SA foreshocks) and ULF
magnetic pulses (ULF foreshocks) observed in Karimshino station in addition
to seismic foreshocks. Such analysis is produced for about 40 rather strong
and nearby isolated earthquakes during 2 years of recording. It is found
that occurrence rate of SA foreshocks increases in the interval (-12, 0 h)
before main shock with 3-times exceeding of background level in the
interval (-6, -3 h), and occurrence probability of SA foreshocks
(pA~75%) is higher than probability of seismic foreshocks (ps~30%)
in the same time interval.ULF foreshocks are masked by
regular ULF activity at local morning and daytime, nevertheless we have
discovered an essential ULF intensity increase in the interval (-3, +1 h)
at the frequency range 0.05-0.3 Hz. Estimated occurrence probability of ULF
foreshocks is about 40%. After theoretical consideration we conclude: 1)
Taking into account the number rate of SA foreshocks, their amplitude and
frequency range, they emit due to opening of fractures with size of
L=70-200 m (M=1-2); 2) The electro-kinetic effect is the most promising mechanism
of ULF foreshocks, but it is efficient only if two special conditions are
fulfilled: a) origin of fractures near fluid-saturated places or liquid
reservoirs (aquifers); b) appearance of open porosity or initiation of
percolation instability; 3) Both SA and ULF magnetic field pulses are
related to near-distant fractures (r<20-30 km); 4) Taking into account
number rate and activation period of seismic, SA and ULF foreshocks, it is
rather probable that opening of fractures and rupture of fluid reservoirs
occur in the large preparation area with horizontal size about 100-200km. |
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