Refraction Microtremor (ReMi) for Shear Velocity

Refraction Microtremor (ReMi) for Shear Velocity
The Most Efficient Shallow Shear-Velocity Estimates

July 18, 2005 John Louie of the CEMAT project at the Nevada Seismological Lab announces a radically new and simple way to estimate shear velocity in-situ to depths as great as 100 meters (300 ft). Louie's team at UNR has measured more than 400 sites in the last 4 years.

Archive of Site Measurements

Optim LLC, a Nevada software developer, has released a full desktop ReMi analysis and modeling package. SeisOpt^®ReMi^TM technology has been licensed to dozens of geotechnical consultants and agencies. Per-site and unlimited licenses are available. Please contact sales@optimsoftware.com for more information.

You simply record noise from your site, on your existing seismic refraction gear. With no seismic source required, you can collect good data at the noisiest urban sites using two person-hours or less. It is now possible to get a quality shear-wave assessment of shallow earthquake site effects in just a few hours, at one-tenth the cost of a logged borehole.

Surveying Seismic Microzonation in Urban Areas presentation; also as Powerpoint Package and Powerpoint file.
Earthquake Hazard Surveys Across Urban Basins Project pages.
Read a published journal paper proving this technique against borehole and microtremor data.
Read the ReMi Field Tutorial.
View a presentation to the Seismological Society of America, April 2001.
Projects, Papers, and Presentations Involving ReMi, April 2004 list.
Read case histories on:
- What if I only have 12-channel data?
- Getting Vs from refraction blast records
- Getting Vs at So. Calif. strong motion sites (PDF poster or page-size PDF poster)

Step One: Fast, Easy Data Collection

All you need is 24-channel digital refraction gear with 8-to-12 Hz single phones. Put the cable across your site in a line 200 m (600 ft) long, with about 8 m (25 ft) spacing between phones. Take 3 to 10 records of background noise, 20-60 seconds long each. That's it! You might be able to measure four sites in one 8-hour shift.

Shear-velocity analysis of other types of data-collection geometries and other types of records can still work. (Multi-phone reflection groups and stacked hammer records probably won't.) Read all about it in the ReMi Field Tutorial.

Step Two: Send Your Data Files

A commercial data-analysis package was released by Optim LLC in June 2002. To have us evaluate your data, please contact sales@optimsoftware.com. Please specify your own contact information, as well as the spacing between the geophones and the time sampling interval, for double-checking. Data files in SEG-2, SEG-Y, or SEG-D are easiest to work with; contact us for other formats.