A new approach to liquefaction hazard zonation: Application to Laoag City,Northern Philippines

To help mitigate liquefaction hazards in the Philippines, an inexpensive yet effective approach to liquefaction hazard zonation was developed in this study. The proposed approach is also useful in other areas especially where funds for more rigorous procedures may not be available. The approach utilizes the geomorphology-based criteria to identify liquefaction-prone deposits based on geology and grain characteristics, and generate a preliminary liquefaction susceptibility map. Then, microtremor recordings, popularly used in site effect estimation, are gathered to derive qualitative information on the density and thickness of these deposits and generate a site classification map. This latter map is also essentially a ground shaking hazard map in that it shows those areas where thick, soft deposits likely to amplify and prolong the duration of ground motion can be found. Therefore, it also identifies areas where seismic demand can be high that the possibility of liquefaction being triggered is likewise high. Combining the two maps, an integrated liquefaction hazard zonation map is produced which provides not only an improved characterization of the soils’ capacity to resist liquefaction but also integrates qualitative information on the seismic demand on these deposits as well. With information about the relative thickness of the deposits, the severity of potential damage can likewise be inferred from the map since thicker deposits relate to more serious damage. The proposed approach was applied to Laoag City, Northern Philippines, where it was shown to reliably identify areas that are vulnerable to the hazard.     

Analysis of faulting in porous sandstones

Faults in porous sandstones occur in three forms: deformation bands about 1-mm thick and tens of m long and across which offsets are a few mm; zones of deformation bands constituted of many closely spaced deformation bands across which offsets are a few cm or dm; and slip surfaces, that is, distinct surfaces within zones of deformation bands across which offsets are a few m to a few tens of m. Deformation bands represent highly localized deformation; analogous localization within a field of homogeneous deformation is theoretically possible in inelastic materials with certain ranges of constitutive parameters. Crushing and consolidation of sandstone within a band cause the material there to become stiffer than the surrounding porous sandstone. A zone of deformation bands behaves mesoscopically much as a stiff inclusion in a soft matrix. According to the constitutive model assumed to investigate the formation of deformation bands, an instability can develop, and strain increments within the zone of deformation bands can become boundlessly large when the far-field stresses reach critical values. This instability is here associated with the formation of slip surfaces.     

Increasing numerical efficiency of iterative solution for total least-squares in datum transformations

Cartesian coordinate transformation between two erroneous coordinate systems is considered within the Errors-In-Variables (EIV) model. The adjustment of this model is usually called the total Least-Squares (LS). There are many iterative algorithms given in geodetic literature for this adjustment. They give equivalent results for the same example and for the same user-defined convergence error tolerance. However, their convergence speed and stability are affected adversely if the coefficient matrix of the normal equations in the iterative solution is ill-conditioned. The well-known numerical techniques, such as regularization, shifting-scaling of the variables in the model, etc., for fixing this problem are not applied easily to the complicated equations of these algorithms. The EIV model for coordinate transformations can be considered as the nonlinear Gauss-Helmert (GH) model. The (weighted) standard LS adjustment of the iteratively linearized GH model yields the (weighted) total LS solution. It is uncomplicated to use the above-mentioned numerical techniques in this LS adjustment procedure. In this contribution, it is shown how properly diminished coordinate systems can be used in the iterative solution of this adjustment. Although its equations are mainly studied herein for 3D similarity transformation with differential rotations, they can be derived for other kinds of coordinate transformations as shown in the study. The convergence properties of the algorithms established based on the LS adjustment of the GH model are studied considering numerical examples. These examples show that using the diminished coordinates for both systems increases the numerical efficiency of the iterative solution for total LS in geodetic datum transformation: the corresponding algorithm working with the diminished coordinates converges much faster with an error of at least 10^-5 times smaller than the one working with the original coordinates.