Governmental Roles and Responsibilities Related to Underground Injection and Induced Seismicity - Induced Seismicity Potential in Energy Technologies - page 108

BOX 4.2
Temporary Seismic Array Acquisition and Processing Cost Estimates
In the event of a felt induced seismic event, a temporary seismic network may be installed to augment
the regional network or to record the events within the temporary network. This involves installing sensitive
seismic instruments around the area of interest to record small earthquakes that are typically difficult to detect
on more than a few instruments within a standard regional array. By augmenting the regional seismic stations
with a dense temporary seismic network, seismologists can carry out detailed analyses on the earthquake
waveforms and improve the earthquake location accuracy in the subsurface. Additionally, if the data and
station coverage around an induced seismic event is appropriate, a better understanding of the earthquake's
size and failure mechanism can be determined. The cost of a temporary seismic array including the array
deployment, operation, and data analyses will depend on the number of stations, the location of the study
area, the length of the study period, and the overall goals of the seismic monitoring project.
A variety of instruments is commercially available for recording small earthquakes. Broadband instruments
specialize in recording a broad spectrum of waveforms from 120 to 175 Hz. Short-period instruments are
equipped to record only high frequencies, in general > 1 Hz. A complete broadband station with recorder,
geophone, and assorted auxiliary equipment costs around $25,000, and a short-period recorder is slightly
less at approximately $20,000 (2011 cost estimates). Eight to 10 instruments are typically deployed for a
small temporary seismic array, but as many as 20 instruments are deployed for more detailed earthquake
surveys. The network sensitivity is often measured by how small an event can be recorded and located, and
the array design will depend on sensitivity required for the study (for example, to record and locate an event
down to M 0). Hence, for a temporary seismic array, instrumentation costs alone run from $120,000 to
$370,000. The seismic instruments can be reused after the study is completed; some minor costs are associ-
ated with instrument maintenance and storage.
The expenditure associated with installing and running the temporary seismic array will depend on the
location of the array and the length of the deployment. Estimated costs for a 150-day deployment are approxi-
mately $100,000, which includes the mobilization, demobilization, equipment setup, tie in with existing seismic
network, and charges for data telemetry. The seismic instrumentation is very sensitive to ground motion, and
geophones cannot be installed in areas with high background noise, such as freeways, busy urban areas,
factories, etc., as they will be saturated with noise and unable to record seismic signal from small earthquakes.
In noisy areas the seismic instruments may have to be placed in shallow boreholes (typically 200 to 400 feet
deep), which will add additional cost to the array installation, which is not included in the price listed above.
Detailed analysis of the seismic data by qualified seismologists is required to determine earthquake
hypocenters and magnitudes, estimate location errors, and determine the type of failure (focal mechanism or
moment tensor inversion). The cost for the work will depend on the detail required; cost estimates for profes-
sional analysis for a 6-month seismic deployment is in the $200,000 to $300,000 range for a university-based
project. Commercial companies—national laboratories, for example—are available to provide these types
of services and prices will vary depending on the project scope. Thus the total cost, including purchasing
seismic instruments and installing and operating the array for a 150-day deployment with 8 to 12 instruments
is estimated at $400,000 to $800,000.
Less costly recording instruments are being developed that could significantly drive down the cost of an
instrument to less than $1,000 to $3,000 per site (Hutchings et al., 2011); however, the type of instrumentation
used will depend on the goal of the study. Overall instrumentation is a minor cost compared to the overall
deployment and interpretation of the seismic data.