In Glendale, we often see site conditions flip within half a block—dense alluvium near Brand Boulevard giving way to softer sediments as you move toward the Los Angeles River channel. That shift matters for seismic design. The MASW method maps shear wave velocity profiles without drilling, using an array of geophones and a sledgehammer or weight-drop source. For projects in the 91202 through 91208 zip codes, the resulting VS30 value feeds directly into ASCE 7 site classification, which determines the design ground motion. The city’s position at the eastern edge of the San Fernando Valley, combined with the proximity of the Verdugo Fault, means a generic soil assumption is never safe. Our field crew runs 1D and 2D MASW lines on undeveloped parcels, parking lots, and even narrow residential lots where a drill rig simply cannot fit.
VS30 is not a soil property—it’s a site-response proxy. In Glendale’s basin-edge zones, a single VS30 number can mask a strong impedance contrast at 15 meters.
Scope of work in Glendale California
Risks and considerations in Glendale California
ASCE 7-22 Section 20.3 requires site classification based on the average shear wave velocity in the upper 30 meters. Guessing—or defaulting to Site Class D without data—is the fastest way to trigger a plan-check rejection at Glendale’s Building & Safety division. We have seen projects along San Fernando Road where assumed Site Class D was used in preliminary design, only for MASW results to show VS30 below 180 m/s, requiring a full Site Class E redesign of the foundation system. The IBC also ties the seismic design category to site class; a softer site can push an ordinary building into a higher risk category, triggering additional detailing requirements under ASCE 7 Chapter 12. In the Verdugo Fault zone, where rupture directivity and basin-edge effects amplify short-period motion, the soft-soil amplification factors in ASCE 7 Table 11.4-2 become critical. A field-measured VS30 eliminates the multiplier uncertainty and gives the structural engineer defensible numbers for base shear calculation.
Our services
We run the survey, process the data, and deliver a signed report ready for plan check. Every project gets a senior geophysicist reviewing the dispersion picks.
VS30 Site Classification
Active-source MASW line with 24–48 geophones, dispersion analysis, and 1D shear-wave velocity profile. Report includes VS30 per ASCE 7 and IBC tables.
2D MASW Cross-Sections
Multiple shot points along a spread to build a 2D stiffness image. Useful for mapping lateral variability in Glendale’s alluvial fans and buried channel deposits.
Combined MASW + Refraction
Simultaneous P-wave seismic refraction and surface-wave acquisition on the same spread. Cross-validates layer geometry and flags hidden low-velocity zones.
Downhole Seismic Verification
For critical structures, we pair MASW with downhole PS suspension logging in a cased borehole, providing direct interval velocities to calibrate the surface-wave inversion.
Common questions
How much does an MASW survey cost for a single-family lot in Glendale?
For a standard residential parcel requiring one or two MASW lines, the fee generally runs from US$1,480 to US$3,170 depending on access, array length, and whether we combine it with seismic refraction. Steep hillside lots in the Verdugo foothills may add mobilization time.
Does the City of Glendale accept MASW for site classification instead of borings?
Yes. Glendale Building & Safety follows the California Building Code, which references ASCE 7 and permits shear-wave velocity measurements by geophysical methods, including MASW, to establish Site Class A through F. We provide the stamped report and the raw dispersion data if the plan checker requests it.
What happens if my VS30 falls in Site Class E?
Site Class E (VS30 below 180 m/s) triggers higher seismic design forces under ASCE 7. The structural engineer must account for amplified spectral accelerations, which often means stronger shear walls, larger footings, or a shift to a mat foundation. We can also run a site-specific ground response analysis to refine the design spectrum instead of using the default code values.
How long does the field work take and what access do you need?
A typical two-line MASW survey takes half a day. We need a clear run of about 50 to 70 meters for the geophone spread. The source is a sledgehammer or a trailer-mounted weight drop; no drilling, no water, no heavy track equipment. We work on graded pads, asphalt parking, and compacted dirt without trouble.
Can MASW see how deep the Verdugo Fault basin sediments go?
MASW penetration depth depends on the longest wavelength we can generate. With a weight-drop source and a 70-meter spread, we typically resolve to 30–35 meters—enough for VS30. For deeper basin structure beyond 50 meters, we recommend a passive-source microtremor array or a downhole suspension log in a deep boring, which we can arrange as a follow-up investigation.