www.sgc.com.auwww.sgc.com.au

PASSIVE SEISMIC (HVSR)

SARA Electronic InstrumentsSouthern Geoscience Consultants is the agent in Australia and Canada of SARA Electronic Instruments. SARA manufactures instrumentation for passive and active seismological, geophysical, engineering, and vibration studies, providing cost-effective solutions for earthquake monitoring, exploration, soil investigations, and risk assessment. SARA’s offerings include the full range of seismological equipment, including mono-,bi-, and triaxial broadband seismometers, the Digital Array modular real-time network, the DoReMi digital telemetry system for near-surface and engineering applications, and borehole sensors. Additionally, SARA offers a range of custom software solutions for survey planning and data processing and visualisation.

GeoBox makes the differenceFor data acquisition, SGC uses the versatile and lightweight SARA GeoBox. The GeoBox contains a high-accuracy three component seismometer and all electronics required to sample, digitize, and transmit the data. The GeoBox’ performance is excellent and results compare positively with those obtained with other equipment; resonance frequencies are defined in great detail and the noise floor is demonstrably low. The GeoBox has the most user-friendly interface on the market: the raw data and a preliminary HVSR plot are visualized in real time on a field tablet allowing for quality control and survey optimisation during acquisition. In combination with SGC’s proprietary software, which is designed for efficient processing and visualisation of large datasets, the GeoBox is the ideal tool for HVSR passive seismic surveys.

The Passive Seismic method uses ambient noise as a seismic source and is a rapid and completely non-disturbing method for the exploration, hydrogeological, environmental and construction industries. Utilizing the horizontal-to-

vertical spectral ratio, it can be used for measuring depth to bedrock and other stratigraphic boundaries, paleochannel mapping, site response analysis, and geotechnical material property assessment amongst other applications.

Southern Geoscience Consultants - HEAD OFFICE39 Richardson Street, West Perth, WA 6005 AustraliaT: +61 (8) 6254 5000 E: geophysics@sgc.com.au

Southern Geoscience Consultants - AMERICASSuite 401, 15 Toronto Street, Toronto, Ontario, M5C 2E3, CanadaT: +1 (416) 407 6355 E: geophysics@sgc.com.au

www.sgc.com.auwww.sgc.com.au

GEOBOX SPECIFICATIONSPower supply: embedded batteryBattery life: up to 10 hoursNumber of channels: 3 24bitOperating temperature: -20 to +75°CSensor availability: 4.5, 2.0, 1.0, 0.5, 0.2HzOptional: GPS for time synchronization

Solutions, instruments and software for seismology,

geophysics and vibrometry

APPLICATIONSDepth to bedrock mappingGeoBox passive seismic data is frequently used to estimate the thickness of overburden. For strong contrasts in acoustic impedance, the horizontal-to-vertical spectral ratio (HVSR) of the ground motion displays a resonance peak, the frequency of which depends on the depth to the contrast and the shear wave velocity of the overburden. Where paleochannels are incised in bedrock, the HVSR method is an efficient way for targeting drilling locations.

Geotechnical engineering propertiesFor structures sensitive to liquefaction or other forms of deformation and collapse, it is critical to understand material strength. The joint inversion of HVSR and MASW dispersion curves are a rapid and reliable way to obtain Vs profiles across a site. HVSR Vs data also provide valuable complimentary information to CPT(u) and shear-wave seismic data.

Site response micro-zonationDetermination of a soil’s resonance frequency and amplification factor can save lives, as was tragically proven in 1985. Amplitude amplification of acoustic energy (originating from an earthquake at distance) in the soft soils below Mexico City caused enormous damage. Passive seismic surveys are now routinely employed in tectonically active areas to prepare cities by highlighting vulnerable areas.

Modal analysisModal analysis is signal processing aimed at identifying the vibrational modes of a structure. It provides experimental evidence on the mechanical properties of the structure and can identify potential design problems. Using modal analysis the dynamic properties of a structure, including the natural vibrations and torsional motion induced by human activities or natural excitation phenomena like wind, are measured.

When employed on different levels of a building or structure, modal frequencies can be derived and compared with soil resonance frequencies.

MORE FROM SARACritical infrastructure monitoringThe S.S.E. system is a turnkey solution for monitoring complex structures like dams or high-rises. It puts in action an automatic process for evaluating (within seconds) if a seismic event impacted the structure. As soon as an event is detected, the ESCAP software module performs corrections and calculates seismological indices and a response spectrum relevant for assessing structure vulnerabilities. If necessary, alert messages are sent. Operators can monitor the real-time evolution of the seismic sequence, analyse velocity, acceleration and displacement, and evaluate structural impacts through 3D particle motion and force vector visualisation.VelBoxThe VelBox is a tri-axial seismometer with similar functionality as the GeoBox but with menu-based operation and internal storage, making it a fully stand-alone solution for passive seismic surveys.DoReMi seismographThe DoReMi is a fully modular seismograph with a very high quality/price ratio and state-of-the-art features, including digital telemetry, embedded batteries, and digitization along the cables to reduce EM noise and cross talk. The DoReMi can be used for all active (MASW, Refraction, Reflection, Downhole) and passive seismic (ReMi, ESAC/SPAC) and for HVSR and structural surveys.

For more information On the products on offer or a price list contact us at geophysics@sgc.com.au