Timing and Recording
Timing is critical when using recording systems that use absolute time (non-cabled). It is important to understand how to time shots based on source types. Select the link to see available options (explosive initiation systems will require supervision due to liability reasons).
Verif-i GPS Synchronizer
These can be used with hammer, accelerated weight drop, marine sources, explosive and vibratory sources (whenever absolute timing is needed). We have 4 of the older units and 4 of the Gen2 units in inventory. The manual linked below works for the current units.
EVR-2
These can be used with hammer, accelerated weight drop, marine sources, explosive and vibratory sources (whenever absolute timing is needed). Works with TTL/Pulse triggers and open/closed circuit (hammer). These are designed to be used with phone or tablet app. We have 3 of these units in inventory. The manual linked below works for the current units.
Shot Boxes
These boxes are generally used with high and low explosive sources. The time base is UTC. We have 6 units. The shooting circuit has been redesigned and built and put into the old boxes.
Trigger Switches
We have high sensitivity switches for hammer work and low sensitivity switches to be used with accelerated weight drop sources.
Point Sources
The chart above shows calculated source energies related to commonly used sources. The actual energy transmitted into the earth will be largely related to the source coupling. Attenuation is related to the medium in which the seismic waves travel.
Hammer
This is a sledgehammer hitting a metal plate to induce elastic waves into the ground.
Accelerated Weight Drop
A source attached to a vehicle that uses a spring or high gas pressure to accelerate a mass into a plate coupled with the ground. We have the United Service Alliance A200 P&S, and the Propelled Energy Generator (PEG-40Kg) source. The specifications can be found in the link below.
Learn more about Accelerated Weight Drops
PEG-40Kg – EPIC
Betsy Seisgun
Uses a blank 8 or 12 Ga shotshell placed underground (~18”) to fire, creating elastic energy.
Explosive
Explosive sources typically range from 150g to 907kg. They generally require drilling small to large holes depending on shot size. We have licensed and credentialed personnel to transport, store and explosives onsite. This lowers large transportation costs and storage issues associated with many projects.
Source Comparison and Testing
In 2017, there was a decrease in the funding rate of large crustal scale seismic projects. However, the demand for smaller scale projects increased leading to source comparison testing. This source comparison test does an approximate side-by-side comparison of small point sources related to shallower seismic projects. The testing was completed at the SSF test facility in West Texas (below). All sources (red dots below) were recorded with 25 Reftek RT-125A recording instruments using 4.5Hz geophones (green dots below). All locations were surveyed with RTK GPS for position accuracies less than 50mm (2″).
The mechanical sources included 5.5kg (12lb.) and 9kg (20lb.) hammers, PEG-40 (below left), A200 P&S
(below right, P-configuration). The chemical sources included shotgun (8 gauge, 400 grain shotshell), and 151g pentolite explosive charges. Mechanical sources were tested at the ground surface (same location). The chemical sources required drilling 63.5mm (2.5″) diameter holes to 0.45m (18″) below ground surface (bgs) for the shotgun to 1.1m (3.5′) bgs for the explosive charges (not same location due to ground disturbance). Drilling was done using “Little Beaver” drill.
The shot gathers above are unnormalized, unfiltered and stacked (5 shots) for apples-to-apples. A. Shot gather using a 5.5kg (12lb.) hammer on a 19x19x1.9cm (7.5″x7.5″x3/4″) aluminum plate. B. Shot gather using a 9.1 kg (20lb.) hammer on a 19x19x1.9cm (7.5″x7.5″x3/4″) aluminum plate. C. Shot gather using a PEG-40 (36kg, (80lb.)) accelerated weight drop on a 46x46x2.5cm (18″x18″x1″) aluminum plate. D. Shot gather using a A200 P&S (98kg, (216lb.)) accelerated weight drop with nitrogen spotting set at 1,900psi. E. Shot gather using Betsy seisgun with 8ga., 26g (400gr) blanks 0.5m (18″) bgs. F. Shot gather using 151g (1/3lb.) pentolite charge approximately 1.1 (3.5′) bgs.
The plot above is related to the mechanical sources (hammers and accelerated weight drops). It shows median amplitude vs. frequency for time window 0 to 1 second for the related shots. The individual shots were stacked (sum of 5 shots) to show increased amplitude with better signal to noise ratio (real data adds and noise subtracts). These sources are very easy to stack at the same surface location.
The plot above is related to the chemical sources (shotgun blanks and pentolite charges). It shows median amplitude vs. frequency for time window 0 to 1 second for the related shots. This plot shows individual shots and stacked shots (sum of 5 shots) to show increased amplitude with better signal to noise ratio (real data adds and noise subtracts). These sources are not easy to stack due to damage related to firing. They also would require drilling multiple drill holes which is very time consuming.
The plot above is related to the chemical sources (shotgun blanks and pentolite charges) and mechanical sources (hammers and accelerated weight drops). In order to maintain apples-to-apples comparison, the chemical shots were not stacked and the mechanical shots were stacked but divided by 5 (stk/5) to maintain relative amplitudes. Generally, chemical shots are done with one charge and mechanical shots are stacked to improve signal to noise ratio. It shows median amplitude vs. frequency for time window 0 to 1 second for the related shots.
The plot above is the median spectral amplitude ratio vs. frequency of all sources from the plot “Chemical & Mechanical Sources” related to a single 151g pentolite shot. This gives a good comparison of amplitude and frequency of the smaller shots related to the largest (151g pentolite). It is very important to note that the A200 P&S source has higher amplitudes in the frequencies range between 90 to 110Hz related to the pentolite shot and higher than the shotgun above 50Hz.
Vibratory Sources
We do not contain these sources in the inventory. However, we have agreements with other agencies such as Natural Hazards Engineering Research Infrastructure (NHERI) and New Mexico Institute of Mining and Technology (NMT).
NHERI
NHERI is located on the University of Texas at Austin campus. The equipment facility is not located on the main campus. However, it is located in Austin, Texas, nearby. They maintain an assortment of P & S vibratory vehicles. Prices and associated costs can be found here.
Learn more about NHERI
Experimental Protocol (Prices)
NMT
NMT is located in Socorro, New Mexico. They have an Industrial Vehicles International (IVI) mini-vibe. This is a trailer-mounted vertical only vibrator with a 4500-lb. force. Water tanks are included on the trailer to add weight. The imaging depth is generally 600 – 800 meters.
