1710 W MARINE VIEW DR Geotech Report 2023-12-29

GeoEngineers, Inc. -2 - 111-0920.000 1. OBJECTIVE Global Geophysics LLC conducted a MASW survey along 5 transects and one MAM on September 20, 2021 around 1716 Marine View Drive, Everett, WA. The goal of this investigation was to study the lateral variation of the soft sediment and the average shear wave velocity to a depth of 100 feet. This report provides the methods, instrumentation, data collection and processing procedures, results, and analysis of this investigation. 2. INTRODUCTION Surface waves are a special type of seismic wave whose propagation is confined to the near surface medium. The depth of subsurface penetration of a surface wave is directly proportional to its wavelength. In a non -homogeneous medium, surface waves are dispersive, i.e. each wavelength has a characteristic velocity stemming from subsurface variations in the soils and rocks. The velocity that the surface waves' wavelengths propagate through the subsurface is related to the shear wave (S-Wave) velocity of the subsurface. If the S-Wave velocity varies with depth, so will the surface wave's wavelength velocity. Analysis of how the wavelength varies, or dispersion, allows us to estimate the S-Wave velocity as it passes through the subsurface. The S-Wave velocity of the subsurface can then be used to infer useful characteristics such as the rock/soil type, stratigraphy, and soil conditions. Average S-Wave velocities to a depth of 100ft (30m) are known as Woo (Vs3o) and are sorted into classes by the International Building Code (IBC) to provide valuable earthquake engineering design information. These classes are shown here: Class Name Ground Description Vsioo Vs30 A Hard Rock >5000ft/s >1500m/s B Rock 5000ft/s to 2500ft/s 1500m/s to 760m/s C Dense Soil or Soft Rock 2500ft/s to 1200ft/s 760m/s to 360m/s D Stiff Soil 1200ft/s to 600ft/s 360m/s to 180m/s E Soft Soil <600ft/s <360m/s F Needs site specific evaluation NA NA Surface waves can be utilized in both active and passive deployments. Multichannel Analysis of Surface Waves (MASW) comprises most active deployments while Microtremor Array Measurements (MAM) are the primary method to collect passive data. MASW arrays are typically linear while MAM arrays can be linear (often known as refraction microtremor, or ReMi, when linear) but generally perform better when deployed in 2D orientations (triangular, circular, T-shaped, or L-shaped arrays). Another passive method employed is the Horizontal over Vertical Spectral Ratio (HVSR) which utilizes a single geophone sensitive to motion in three directions (vertical, east -west, and north - south). For this project, the seismic survey was deployed at the location shown on Figure 1. Global Geophysics