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Earthquake rupture dynamics frozen in exhumed ancient faults
Language
English
Obiettivo Specifico
3.1. Fisica dei terremoti
Status
Published
JCR Journal
JCR Journal
Peer review journal
Yes
Title of the book
Issue/vol(year)
/436 (2005)
Pages (printed)
1009-1012
Issued date
2005
Abstract
fault zone14. Fault segments carrying only pseudotachylytes (that is,
Most of our knowledge about co-seismic rupture propagation is
derived from inversion and interpretation of strong-ground- not associated with cataclastic precursor) have displacements of less
motion seismograms1–3, laboratory experiments on rock4,5 and than 1.5 m, which are typical of seismic fault ruptures of about 10 km
rock-analogue material6, or inferred from theoretical and numeri- in length17. Field and microstructural data indicate that pseudota-
cal elastodynamic models7–9. However, additional information on chylyte is produced at the final stage of fault slip14. Evidence of
dynamic rupture processes can be provided by direct observation multiple generations of pseudotachylytes is rare along the Gole
of faults exhumed at the Earth’s surface10. Pseudotachylytes Larghe fault14; pseudotachylytes within each individual fault segment
(solidified friction-induced melts11,12) are the most certain fault- are therefore the result of a single seismic rupture.
rock indicator of seismicity on ancient faults13. Here we show how Many pseudotachylyte veins were injected into the host tonalite
the asymmetry in distribution and the orientation of pseudo- from pseudotachylyte-bearing fault segments; an example of a fault
tachylyte-filled secondary fractures around an exhumed fault can segment with injection veins is shown in Fig. 2. We measured the
be used to reconstruct the earthquake rupture directivity, rupture orientation of 624 injection veins that branch off 28 different fault
velocity and fracture energy, by comparison with the theoretical segments, in exposures sub-parallel to the fault slip direction. Linear
dynamic stress field computed around propagating fractures. In fault segments that were at least 2–3 m away from the closest segment
particular, the studied natural network of pseudotachylytes is were selected for the measures, to avoid potential perturbations due
to fault irregularity18 and interference with neighbouring faults. The
consistent with a dominant propagation direction during repeated
cumulative data from all measures (Fig. 3) reveals two dominant
seismic events and subsonic rupture propagation close to the
orientations of injection veins, at about 30–2108 (referred to as set 1)
Rayleigh wave velocity.
and 90–2708 (set 2) with respect to the fault trace. Both vein sets are
asymmetrically distributed with respect to the fault trace with
distinct dominance (67.7%) of the veins intruded into the southern
bounding block. The veins of set 1 (mostly less than 2 mm thick and
less than 50 cm long) intruded pre-existing minor cataclastic faults
Most of our knowledge about co-seismic rupture propagation is
derived from inversion and interpretation of strong-ground- not associated with cataclastic precursor) have displacements of less
motion seismograms1–3, laboratory experiments on rock4,5 and than 1.5 m, which are typical of seismic fault ruptures of about 10 km
rock-analogue material6, or inferred from theoretical and numeri- in length17. Field and microstructural data indicate that pseudota-
cal elastodynamic models7–9. However, additional information on chylyte is produced at the final stage of fault slip14. Evidence of
dynamic rupture processes can be provided by direct observation multiple generations of pseudotachylytes is rare along the Gole
of faults exhumed at the Earth’s surface10. Pseudotachylytes Larghe fault14; pseudotachylytes within each individual fault segment
(solidified friction-induced melts11,12) are the most certain fault- are therefore the result of a single seismic rupture.
rock indicator of seismicity on ancient faults13. Here we show how Many pseudotachylyte veins were injected into the host tonalite
the asymmetry in distribution and the orientation of pseudo- from pseudotachylyte-bearing fault segments; an example of a fault
tachylyte-filled secondary fractures around an exhumed fault can segment with injection veins is shown in Fig. 2. We measured the
be used to reconstruct the earthquake rupture directivity, rupture orientation of 624 injection veins that branch off 28 different fault
velocity and fracture energy, by comparison with the theoretical segments, in exposures sub-parallel to the fault slip direction. Linear
dynamic stress field computed around propagating fractures. In fault segments that were at least 2–3 m away from the closest segment
particular, the studied natural network of pseudotachylytes is were selected for the measures, to avoid potential perturbations due
to fault irregularity18 and interference with neighbouring faults. The
consistent with a dominant propagation direction during repeated
cumulative data from all measures (Fig. 3) reveals two dominant
seismic events and subsonic rupture propagation close to the
orientations of injection veins, at about 30–2108 (referred to as set 1)
Rayleigh wave velocity.
and 90–2708 (set 2) with respect to the fault trace. Both vein sets are
asymmetrically distributed with respect to the fault trace with
distinct dominance (67.7%) of the veins intruded into the southern
bounding block. The veins of set 1 (mostly less than 2 mm thick and
less than 50 cm long) intruded pre-existing minor cataclastic faults
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