 |
| Titel |
Nonlinear seismology a reality. The quantitative data |
| VerfasserIn |
G. Marmureanu, C. O. Cioflan, A. Marmureanu |
| Konferenz |
EGU General Assembly 2012
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250060247
|
|
|
|
|
|
| Zusammenfassung |
| Nonlinear effects in ground motion during large earthquakes have long been a controversial
issue between seismologists and geotechnical engineers. The central point of the discussion
in last 10-15 years was whether soil amplification is function of earthquake magnitude.
Laboratory tests made by using Hardin or Drnevich resonant columns consistently show the
decreasing of dynamic torsion function(G) and increasing of torsion damping function(D%)
with shear strains(γ) induced by deep strong Vrancea earthquakes; G = G(γ), respectively,
D%= D%(γ),therefore nonlinear viscoelastic constitutive laws are required. Nonlinear
amplification at sediments sites appears to be more pervasive than seismologists used
to think-¦Any attempt at seismic zonation must take into account the local site
condition and this nonlinear amplification (Aki, A., Local Site Effects on Weak and
Strong Ground Motion, Tecto-nophysics, 218, pp.93-111, 1993). The difficulty to
seismologists in demonstrating the nonlinear site effects has been due to the effect being
overshadowed by the overall patterns of shock generation and propagation. In other words,
the seismological detection of the nonlinear site effects requires a simultaneous
understanding of the effects of earthquake source, propagation path and local geological
site conditions. In main ground motion equation, ground displacement u(t) has
general form: u(t)=s(t)*g(t)*i(t),where s(t),g(t) and i(t) are source, propagation and,
respectively, instrument recording functions. The authors, in order to make quantitative
evidence of large nonlinear effects, introduced and developed the concept of the
nonlinear spectral amplification factor (SAF) as ratio between maximum spectral
absolute acceleration (Sa), relative velocity (Sv ), relative displacement (Sd) from
response spectra for a fraction of critical damping (ζ %) at fundamental period or
any other period and peak values of acceleration (amax), velocity (vmax) and
displacement (dmax) ,respectively, from processed strong motion records, that are:(SAF)a=
Samax/amax; (SAF)v = Svmax/vmax; (SAF)d = Sdmax/dmax where: amax = ý(t)max;
vmax = áº(t)max and dmax = x(t)max.The concept was used for last Stress Test asked by
IAEA Vienna for Romanian Cernavoda Nuclear Power Plant, where we recorded
last three deep strong Vrancea earthquakes: August 30,1986(MGR=7.0),May 30
(MGR=6.7) and May 31,1990 (MGR=6.2).The spectral amplification factors were: SAF=
4.07 (MGR=7.0); 4.74(MGR=6.7) and 5.78 (MGR=6.2),function of earthquake
magnitude, which are far of that given in Regulatory Guide 1.60 of the U. S. Atomic
Energy Commission and accepted by IAEA. The present analysis indicates that
the effect of nonlinearity could be very important and if the analysis is made for
peak accelerations, it is 48.87% and for stronger earthquakes it will be bigger. The
authors are coming with new recorded data which will open up a new challenge for
seismologists studying nonlinear site effects in 2-D and 3-D irregular geological
structures, leading them to a fascinating research subject in nonlinear seismology. |
|
|
|
|
|
|