Seismic Wave Propagation in a Very Soft Alluvial Valley: Sensitivity to Ground-Motion Details and Soil Nonlinearity, and Generation of a Parasitic Vertical Component

This paper explores the sensitivity of 2D wave effects to crucial problem parameters, such as the frequency content of the base motion, its details, and soil nonlinearity. A numerical study is conducted, utilizing a shallow soft valley as a test case. It is shown that wave focusing effects near valley edges and surface waves generated at valley corners are responsible for substantial aggravation (AG) of the seismic motion. With high-frequency seismic excitation, 1D soil amplification is pre- vailing at the central part of the valley, while 2D phenomena are localized near the edges. For low-frequency seismic excitation, wave focusing effects are overshadowed by laterally propagating surface waves, leading to a shift in the location of maximum AG toward the valley center. If the response is elastic, the details of the seismic excitation do not seem to play any role on the focusing effects at valley edges, but make a substantial difference at the valley center, where surface waves are dominant. The increase of damping mainly affects the propagation of surface waves, reducing AG at the valley center, but does not appear to have any appreciable effect at the valley edges. Soil nonlinearity may modify the 2D valley response significantly. For ideal- ized single-pulse seismic excitations, AG at the valley center is reduced with increas- ing nonlinearity. Quite remarkably, for real multicycle seismic excitations AG at the valley edges may increase with soil nonlinearity. In contrast to the vertical component of an incident seismic motion, which is largely the result of P waves and is usually of too high frequency to pose a serious threat to structures, the valley-generated parasitic vertical component could be detrimental to structures: being a direct result of 2D wave reflections/refractions, it is well correlated and with essentially the same dominant periods as the horizontal component.

[1]  Amr S. Elnashai,et al.  Analysis of the damage potential of the Kocaeli (Turkey) earthquake of 17 August 1999 , 2000 .

[2]  David R. O'Hallaron,et al.  Earthquake ground motion modeling on parallel computers , 1996, Supercomputing '96.

[3]  J. Lawrence Von Thun,et al.  Earthquake engineering and soil dynamics II : recent advances in ground-motion evaluation : proceedings of the specialty conference , 1988 .

[4]  Bin Zhang,et al.  Simulation of the response of the Marina District Basin, San Francisco, California, to the 1989 Loma Prieta earthquake , 1996 .

[5]  Toshihiro Wakahara,et al.  Seismic Observations and Analysis of Grouped Piles , 1987 .

[6]  G. Gazetas,et al.  Seismic Response of the Pile Foundation of Ohba-Ohashi Bridge , 1993 .

[7]  Kyriazis Pitilakis,et al.  Parametric analysis of the seismic response of a 2D sedimentary valley: implications for code implementations of complex site effects , 2005 .

[8]  I. Anastasopoulos,et al.  Asymmetric ‘Newmark’ Sliding Caused by Motions Containing Severe ‘Directivity’ and ‘Fling’ Pulses , 2011 .

[9]  H. L. Wong,et al.  Surface motion of a semi-elliptical alluvial valley for incident plane SH waves , 1974, Bulletin of the Seismological Society of America.

[10]  Francisco J. Sánchez-Sesma,et al.  Seismic response of three-dimensional alluvial valleys for incident P, S, and Rayleigh waves , 1995 .

[11]  R. Dobry,et al.  Effect of Soil Plasticity on Cyclic Response , 1991 .

[12]  A. Papageorgiou,et al.  Study of the propagation and amplification of seismic waves in Caracas Valley with reference to the 29 July 1967 earthquake: SH waves , 1991 .

[13]  N. Ricker.  The Form and Laws of Propagation of Seismic Wavelets , 1951 .

[14]  I. Kalogeras,et al.  Preliminary Results about the Catastrophic Earthquake of 7 September 1999 in Athens, Greece , 2000 .

[15]  M. D. Trifunac,et al.  Erratum to surface motion of a semi-cylindrical alluvial valley for incident plane SH waves , 1972, Bulletin of the Seismological Society of America.

[16]  Omar Ghattas,et al.  ONE- VS TWO- OR THREE-DIMENSIONAL EFFECTS IN SEDIMENTARY VALLEYS , 1999 .

[17]  Keiiti Aki,et al.  Local Site Effects on Strong Ground Motion , 1988 .

[18]  Kyriazis Pitilakis,et al.  Site effects at Euroseistest—II. Results from 2D numerical modeling and comparison with observations , 2000 .

[19]  Omar Ghattas,et al.  Earthquake Ground Motion and Structural Response in Alluvial Valleys , 1999 .

[20]  Maria I. Todorovska,et al.  Surface motion of shallow circular alluvial valleys for incident plane SH waves-analytical solution , 1991 .

[21]  Akira Ohtsuki,et al.  Effect of lateral inhomogeneity on seismic waves, II. Observations and analyses , 1984 .

[22]  Francisco J. Sánchez-Sesma,et al.  Seismic response of a class of alluvial valleys for incident SH waves , 1988 .

[23]  Edward H. Field,et al.  Spectral amplification in a sediment-filled Valley exhibiting clear basin-edge-induced waves , 1996, Bulletin of the Seismological Society of America.

[24]  George Gazetas,et al.  Topography and Soil Effects in the MS 5.9 Parnitha (Athens) Earthquake: The Case of Adámes , 2002 .

[25]  K. Fishman,et al.  Seismic response for alluvial valleys subjected to SH, P and SV waves , 1995 .

[26]  Marianna Loli,et al.  Soil failure can be used for seismic protection of structures , 2010 .

[27]  I. Ishibashi,et al.  UNIFIED DYNAMIC SHEAR MODULI AND DAMPING RATIOS OF SAND AND CLAY , 1993 .

[28]  Pierre-Yves Bard,et al.  The seismic response of sediment-filled valleys. Part 2. The case of incident P and SV waves , 1980 .

[29]  Akira Ohtsuki,et al.  Effect of topography and subsurface inhomogeneities on seismic SV waves , 1983 .

[30]  Kyriazis Pitilakis,et al.  Site Effects and Design Provisions: The Case of Euroseistest , 2001 .

[31]  L. Pérez-Rocha,et al.  Diffraction of elastic waves by three-dimensional surface irregularities. Part II , 1989 .

[32]  Anastasia Kiratzi,et al.  The 14 August 2003 Lefkada Island (Greece) earthquake: Focal mechanisms of the mainshock and of the aftershock sequence , 2005 .

[33]  Kyriazis Pitilakis,et al.  Site effects at Euroseistest—I. Determination of the valley structure and confrontation of observations with 1D analysis , 2000 .