Empirical Correlation between Standard Penetration Resistance (SPT-N) and Shear Wave Velocity (Vs) for Soils in Metro Manila, Philippines

The measurement of the shear wave velocities (Vs) of soils is an important aspect of geotechnical and earthquake engineering, due to its direct relation to the shear modulus (G), which in turn influences the stress–strain behavior of geomaterials. Vs can be directly measured or estimated using a variety of onsite tests or in a laboratory. Methods such as downhole PS logging require boreholes and may not be logistically and economically feasible in all situations. Many researchers have estimated Vs from other geotechnical parameters, such as standard penetration test resistance (SPT-N), by means of empirical correlations. This paper aimed to contribute to this subject by developing an empirical relationship between Vs and SPT-N. Data from twenty sites in Metro Manila were obtained from geotechnical investigation reports. Vs profiles of the same sites were also acquired using the refraction microtremor method. New empirical relationships were developed for all, sandy, and clayey soil types, using a non-linear regression method that is applicable for Metro Manila soils. Statistical evaluation and comparison of the proposed correlations with other previous works suggested the viability of the empirical model

Shallow structures, interactions, and recurrent vertical motions of active faults in Lingayen Gulf, Philippines

The surface trace of the East Zambales Fault (EZF) and its associated faults in the Lingayen Gulf have been previously mapped but no other characteristics were reported. This study utilized seismic reflection, multi-beam bathymetry, and side scan sonar to characterize the offshore EZF in terms of magnitudes of vertical displacement. Sequence stratigraphy and radiocarbon dates provided age constraints on the recurrence interval within the Holocene.The EZF extends for ∼ 57 km into the gulf, follows a north-northwest trend, and bounds the karstic terrane (west) and fluvio-deltaic deposits (east). Sinistral motion is indicated by: 1) normal and reverse drag geometries, 2) reversal in the sense of throw with depth, 3) flower structure, and 4) right-stepping and the uplift of a pressure ridge named Pudoc Bathymetric High. The Central Lingayen Gulf Fault (CLGF), to the east of EZF, follows the same trend. The Lingayen Gulf Transverse Fault (LGTF), oriented east–west, forms a flower structure with the CLGF. The EZF, CLGF, and LGTF combined form the Lingayen Gulf Fault System, which divides the gulf into five fault blocks where uplift and subsidence locally occurred.A paleo-delta at −60 m yielded an age of 6.8 kyBP, indicating it was formed during the first Holocene highstand. With natural compaction considered, fault-associated subsidence of 46–53 m may have occurred. The average Holocene vertical displacement is 2.1–2.2 m, which translates to a recurrence interval of 320–270 years for the fault system. The faults can likely generate earthquakes with magnitudes 7.5 (EZF), 6.7 (CLGF), and 6.6 (LGTF)