High-speed photography applied to seismic source studies and further issues
| Cosa | seminari |
|---|---|
| Quando | 30/01/2008 da 11:00 al 21:00 |
| Dove | Roma |
| Aggiungi l'evento al calendario |  vCal (Windows, Linux) iCal (Mac OS X) |
30 gennaio 2008 ore 11.00 | Stefan Nielsen, Primo ricercatore Roma 1 | Sala Conferenze - Roma | Sede Centrale autori S. Nielsen, J. Taddeucci, S. Vinciguerra
Several challenging issues about the character of dynamic earthquake
rupture have been recently raised. In particular they concern the
acceptable ranges of stable velocity and the possibility that slip
occurs in short, self-healing pulses. However, it is difficult to
predict the effects of surface roughness and friction complexity and
to include them in simulations with classical numerical tools. In
alternative, we illustrate here a series of novel observations
obtained in laboratory experiments with a photographic method.Two
precut samples were put in contact on their edge, under uniaxial load
of 1-13 kN, at an angle close to instability in order to ensure the
spontaneous triggering of fracture. The samples consist of 8
mm-thickness plates of CR (Columbia Resin, a hard synthetic material
with compressional waves Vp ~ 1800 m/s). An high speed digital camera
with interframe intervals of 10 ?sec acquired image sequences of
fracture propagation. The entire process is monitored, starting from
slow fracture initiation, till acceleration and fully dynamic
propagation at sonic and intersonic velocity. In order to explore a
variety of friction conditions, experiments were performed either: (a)
after surface roughening and insertion of lubricating material at
isolated points along the contact; (b) In plain contact between the
precut smoothed edges. Experiments of type (a) show an elevated degree
of complexity, including re-rupturing episodes on the same surface
within short time intervals, suggesting rapid re-strengthening of the
surface and the formation of self-healing pulses. The more repeatable
experiments of type (b) reveal a consistent set of 3 propagation
velocities Vr: (1) subsonic dynamic propagation (Vr close to the
Rayleigh wave velocity), (2) supershear rupture propagation (Vs < Vr <
Vp) and (3) an extremely slow, but stable propagation velocity (40 <
Vr < 60 m/s), essentially observed after the beginning of instability
but before acceleration toward the dynamic propagation.
rupture have been recently raised. In particular they concern the
acceptable ranges of stable velocity and the possibility that slip
occurs in short, self-healing pulses. However, it is difficult to
predict the effects of surface roughness and friction complexity and
to include them in simulations with classical numerical tools. In
alternative, we illustrate here a series of novel observations
obtained in laboratory experiments with a photographic method.Two
precut samples were put in contact on their edge, under uniaxial load
of 1-13 kN, at an angle close to instability in order to ensure the
spontaneous triggering of fracture. The samples consist of 8
mm-thickness plates of CR (Columbia Resin, a hard synthetic material
with compressional waves Vp ~ 1800 m/s). An high speed digital camera
with interframe intervals of 10 ?sec acquired image sequences of
fracture propagation. The entire process is monitored, starting from
slow fracture initiation, till acceleration and fully dynamic
propagation at sonic and intersonic velocity. In order to explore a
variety of friction conditions, experiments were performed either: (a)
after surface roughening and insertion of lubricating material at
isolated points along the contact; (b) In plain contact between the
precut smoothed edges. Experiments of type (a) show an elevated degree
of complexity, including re-rupturing episodes on the same surface
within short time intervals, suggesting rapid re-strengthening of the
surface and the formation of self-healing pulses. The more repeatable
experiments of type (b) reveal a consistent set of 3 propagation
velocities Vr: (1) subsonic dynamic propagation (Vr close to the
Rayleigh wave velocity), (2) supershear rupture propagation (Vs < Vr <
Vp) and (3) an extremely slow, but stable propagation velocity (40 <
Vr < 60 m/s), essentially observed after the beginning of instability
but before acceleration toward the dynamic propagation.