Experimental setup

The array consisted of 60 40-Hz single-component geophones arranged in a 6-by-10 grid 25 m wide and 45 m long. Figure 1 shows the array's orientation relative to a U.S. Geological Survey high-resolution shotgun-source survey that was performed 2 days prior to this exercise. The array was shifted 1 m northwest of the USGS line to avoid placing geophones on the asphalt road. Figure 1 also shows the location of a deep well that was being drilled at a depth of nearly 150 m during data acquistion.

A manually triggered Geometrics RX-60 seismograph recorded 60 channels at a sample interval of 4 ms; no filters were used. Over two days, this passive experiment produced approximately 170 minutes of 10-second long records and 20 60-second long records. During each of the 60-second records, the first author performed a ``two footed'' stomp at one the geophones along the northeastern and southwestern edges of the array. The array also recorded energy from the intermittant operation of the nearby drill-bit, drill-truck engine, and the gasoline-powered water pump. Figure 2 shows five seconds of recorded data after notch-filtering.

 

arraytest Figure 1 Long Beach passive array. ``Mainline Shotpoints and Geophones'' denote the source and receiver locations for the USGS high-res survey (see text). Approximate locations of the well, drill-truck, and water pump are also shown.

 

strip Figure 2 Five seconds of passive seismic data after notch-filtering.