Investigation of Observed Seismicity 

in the Horn River Basin

BC Oil and Gas Commission - August 2012
The BC Oil and Gas Commission is the single-window 

regulatory agency with responsibilities for regulating 

oil and gas activities in British Columbia, including 

exploration, development, pipeline transportation and 

reclamation.

The Commission’s core roles include reviewing and 

assessing applications for industry activity, consulting 

with First Nations, ensuring industry complies with 

provincial legislation and cooperating with partner 

agencies. The public interest is protected by ensuring 

public safety, protecting the environment, conserving 

petroleum resources and ensuring equitable participation 

in production. 

For general information about the Commission, please 

visit www.bcogc.ca or phone 250-794-5200.

About the 

BC Oil and Gas Commission

Fort St. John 

Fort Nelson

Dawson Creek 

Kelowna

Victoria

www.bcogc.ca

Terms Used in this Report

‘Seismicity’, ‘Seismic Events’ and 

‘Events’ – used interchangeably 

to describe seismograph recorded 

earthquakes caused primarily by 

fault movement.

‘Micro-Seismicity’ – very low 

magnitude events created by 

shear movement or tensile fracture 

during hydraulic fracturing not 

detectable by the Canadian National 

Seismograph Network (CNSN).

‘Microseismic’ – describes both 

the recording and processing of very 

small magnitude events produced 

by hydraulic fracturing.

‘Induced Seismicity’ – generally 

defined as earthquakes resulting 

from human activity. 

‘Stage’ – refers to a hydraulically 

fractured interval along a horizontal 

wellbore, each stage is isolated and 

perforated prior to the injection of 

fluids to hydraulically fracture the 

reservoir rock.

03 Executive Summary 

04 Event Summary 

06 Investigation Overview 

08 Induced Seismicity in B.C.

12 Literature Review

14 Analysis

21 Controls on Seismicity

23 Davis and Frohlich Criteria

25 Findings

26 Recommendations

28 Conclusion

29 References

Table of Contents
This report provides the results of the BC Oil and 

Gas Commission’s (Commission) investigation into 

anomalous seismicity within geographically confined and 

remote areas in the Horn River Basin between April 2009 

and December 2011. The investigation was commenced 

immediately after the Commission became aware of a 

number of anomalous, low-level seismic events which 

were recorded by Natural Resources Canada (NRCan) 

near areas of oil and gas development. Only one of the 

events under investigation had been reported by NRCan 

as “felt” at the earth’s surface. 

In undertaking the investigation, the Commission notes 

that more than 8,000 high-volume hydraulic fracturing 

completions have been performed in northeast British 

Columbia with no associated anomalous seismicity. 

None of the NRCan reported events caused any injury, 

property damage or posed any risk to public safety or the 

environment. 

The investigation was completed by the Commission’s 

geological and engineering staff within the Resource 

Development department, and they benefited from 

consultation with NRCan, the University of British 

Columbia and the Alberta Geological Survey. Data 

was obtained from numerous sources including open 

source information as well as proprietary data acquired 

by oil and gas companies working near the area of the 

investigation. 

Executive Summary

The Commission also acknowledges the professional, 

open and honest exchanges of information and analyses 

between the regulated industry and the investigation team.

The investigation has concluded that the events observed 

within remote and isolated areas of the Horn River Basin 

between 2009 and 2011 were caused by fluid injection 

during hydraulic fracturing in proximity to pre-existing 

faults.

Three sets of events are discussed in the report, the 38 

events reported by NRCan, 216 events recorded by a 

dense array deployed at Etsho and 18 events recorded 

by a dense array deployed at Kiwigana. All these events 

are interpreted to be the result of fault movement.

The Etsho dense array monitored the d-1-D/94-O-8 pad. 

Events, recorded by this array, occurred on microseismic 

plots along linear trends interpreted to be faults. In only 

one instance did a linear seismic swarm overlay a fault 

mapped with 2D or 3D seismic.

Fault maps interpreted from 2D and 3D seismic were 

submitted for the investigation. These showed 12 

mapped faults intersecting five of the 7 d-1-D pad 

wellbores. No events could confidently be linked to 11 of 

these faults, indicating that most of the faults intersected 

either did not slip or did move without generating a 

detectable event. 

Disposal wells were ruled out as a source of the 

seismicity during the investigation. Four disposal wells 

were operating during the period of observed seismicity: 

three at Etsho and one in the Tattoo area. These wells 

were injecting recovered hydraulic fracturing fluids into 

the Mississippian Debolt Formation, 1800 metres above 

the Horn River Group. All event epicentres occurred 

within the Devonian Horn River Group and no fault 

movement was seen in the Debolt Formation. 

The Commission makes seven recommendations based 

on the investigation, which include the submission of 

microseismic reports; establishment of a notification 

and consultation procedure; studying the relationship 

of hydraulic fracturing parameters on seismicity, and 

upgrading and improving B.C.’s seismograph grid 

and monitoring procedures. Improvements to the 

seismographic grid network have already begun through 

funding provided by Geoscience BC. The upgraded grid 

will provide improved monitoring for induced seismicity 

and will form the basis for the monitoring, detection, 

notification and consultation procedure.

In addition, the Commission has initiated a broader study 

with the University of British Columbia to examine factors 

related to the extent, magnitude, impact and control of 

induced seismicity in northeast B.C. The intent of this 

research is to provide insights into predicting the location 

and magnitude of seismic events based on hydraulic 

fracturing parameters and geomechanics and to establish 

protocols for prediction, detection, monitoring and 

mitigation of these events.

Investigation of Observed Seismicity in the Horn River Basin 3
4 Investigation of Observed Seismicity in the Horn River Basin 

Between April 2009 and July 2011, 31 seismic events 

were recorded and located by NRCan in the Etsho area 

of the Horn River Basin in northeast British Columbia 

(Figure 1). Another seven events were recorded near 

the Tattoo area between Dec. 8 and Dec. 13, 2011. The 

observed events ranged in magnitude between 2.2 and 

3.8 ML on the Richter scale as recorded by NRCan 

(Table 1). 

A search of the areas in the National Earthquake Database 

from 1985 to present shows no detected seismicity in the 

Horn River Basin prior to 2009. Two events (1985/09/04, 

3.1ML and 1986/09/28, 2.9ML) located approximately 160 

km south and southwest of Fort Nelson were detected by 

the Canadian National Seismograph Network (CNSN). 

This suggests that similar events occurring in the Horn 

River Basin could have been recorded. Two NRCan 

seismograph stations, part of the CNSN, are currently 

operational in northeast British Columbia. The Bull 

Mountain station near Hudson’s Hope became operational 

in January 1998 and the Fort Nelson station came online 

in 1999. Magnitudes have been processed and reported 

down to approximately 2.0 ML in the Horn River Basin 

since deployment of these two stations. Smaller events 

may have occurred and gone undetected due to the 

detection limitations of the CNSN. While the full extent 

of historical seismicity is not known, the April 2009 to 

December 2011 Etsho and Tattoo events are considered 

anomalous events when considered in full context.

Event Summary

Figure 1: Location of Etsho, Tattoo and Kiwigana areas in the Horn River Basin. Red triangles 

show NRCan reported epicentres, Bovie and Trout Lake Fault zones noted. Liard Basin to west of 

Bovie Fault. Blue star indicates location of Kiwigana seismograph array.

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Northwest Territories

Fort

Nelson

094O11

094O16 094P13

094J15

094P04

094J16

094O06

094O14

094I13

094O02

094J14

094O10 094O09 094P12

094O01

094O03

094O07

094O08

094O15

094P05

HORN

RIVER

BASIN

LIARD

BASIN

B

ovie

Lake

Fault

Trout Lake

Fault Zone

121°45'0"W

121°45'0"W

122°0'0"W

122°0'0"W

122°15'0"W

122°15'0"W

122°30'0"W

122°30'0"W

122°45'0"W

122°45'0"W

123°0'0"W

123°0'0"W

123°15'0"W

123°15'0"W

59°45'0"N

59°45'0"N

59°30'0"N

59°30'0"N

59°15'0"N

59°15'0"N

59°0'0"N

59°0'0"N

Tattoo Field

0 2.5 5 10 15 Kilometers

#* Earthquakes

! Major Cities

" Well Surface Hole

( Well Bottom Hole

Well Directional Survey

Earthquakes NEBC

2009 - 2012

1:500,000

!

!

!

!

Kelowna

Victoria

Fort Nelson

Fort St. John

Tattoo Area

Etsho Area

Kiwigana

^_
Investigation of Observed Seismicity in the Horn River Basin 5

Table 1 provides a summary of the events recorded by NRCan in the Etsho and Tattoo areas that are plotted and shown on Figure 1.

The events in Table 1 were proximate to oil and gas activities employing hydraulic fracture operations when the events occurred.

Table 1 – Magnitude and 

Location of NRCan Seismic Events, 

with date and time. 

Modified from NRCan report.

www.earthquakescanada.nrcan.gc.ca/

 Event # Date Time (UT) Time (Pacific) Correct Date Lat Long Mag Approximate Location

38 2011/12/13 13:17:32 5:17:32 59.84 -122.66 3.1ML 114 km N of Fort Nelson

37 2011/12/12 23:34:12 15:34:12 59.81 -122.68 3.1ML 110 km N of Fort Nelson

36 2011/12/12 07:59:22 23:59:22 12/11/2011 59.82 -122.69 2.9ML 112 km N of Fort Nelson

35 2011/12/11 09:15:57 1:15:57 59.85 -122.69 2.4ML 114 km N of Fort Nelson

34 2011/12/11 02:37:53 18:37:53 12/10/2011 59.87 -122.67 2.9ML 116 km N of Fort Nelson

33 2011/12/10 02:52:34 18:52:34 12/9/2011 59.87 -122.69 2.9ML 117 km N of Fort Nelson

32 2011/12/08 15:28:37 7:28:37 59.81 -122.65 2.8ML 111 km N of Fort Nelson

31 2011/07/14 10:40:32 2:40:32 59.51 -122.20 2.5ML 82 km NE of Fort Nelson

30 2011/07/07 22:46:37 14:46:37 59.49 -122.40 3.1ML 76 km NNE of Fort Nelson

29 2011/07/01 09:32:46 1:32:46 59.54 -122.49 2.6ML 81 km NNE of Fort Nelson

28 2011/06/26 13:17:02 5:17:02 59.56 -122.37 2.7ML 84 km NNE of Fort Nelson

27 2011/06/18 23:02:03 15:02:03 59.82 -121.47 2.8ML 132 km NE of Fort Nelson

26 2011/05/29 08:09:47 0:09:47 59.54 -122.46 3.1ML 81 km NNE of Fort Nelson

25 2011/05/20 06:22:34 22:22:24 5/19/2011 59.51 -122.52 3.0ML 78 km NNE of Fort Nelson

24 2011/05/19 13:13:43 5:13:43 59.47 -122.47 3.3ML 74 km NNE of Fort Nelson

23 2011/05/19 13:05:15 5:05:15 59.49 -122.41 3.8ML 76 km NNE of Fort Nelson

22 2011/05/10 14:16:03 6:16:03 59.51 -122.37 3.5ML 79 km NNE of Fort Nelson

21 2011/05/03 12:56:29 4:56:29 59.51 -122.32 3.2ML 80 km NNE of Fort Nelson

20 2011/04/30 13:27:30 5:27:30 59.46 -122.59 3.1ML 72 km N of Fort Nelson

19 2011/04/28 22:34:51 14:34:51 59.47 -122.47 2.5ML 73 km NNE of Fort Nelson

18 2011/04/07 12:19:20 4:19:20 59.50 -122.51 3.2ML 76 km NNE of Fort Nelson

17 2011/03/04 03:09:05 19:09:05 3/3/2011 59.50 -122.34 3.3ML 78 km NNE of Fort Nelson

16 2010/10/12 21:01:11 13:01:11 59.55 -122.38 3.4ML 83 km NNE of Fort Nelson

15 2010/10/12 19:19:44 11:19:44 59.53 -122.31 3.0ML 83 km NNE of Fort Nelson

14 2010/10/12 17:09:40 9:09:40 59.59 -122.45 3.4ML 87 km NNE of Fort Nelson

13 2010/10/09 10:00:31 2:00:31 59.54 -122.42 3.1ML 82 km NNE of Fort Nelson

12 2010/10/05 22:01:14 14:01:14 59.60 -122.39 3.6ML 88 km NNE of Fort Nelson

11 2010/10/05 13:30:28 5:30:28 59.53 -122.27 3.1ML 83 km NNE of Fort Nelson

10 2010/10/04 11:09:34 3:09:34 59.59 -122.36 2.9ML 88 km NNE of Fort Nelson

9 2010/10/03 08:06:50 0:06:50 59.56 -122.27 3.5ML 86 km NNE of Fort Nelson

8 2010/09/30 12:33:36 4:33:36 59.58 -122.48 3.0ML 85 km NNE of Fort Nelson

7 2010/09/30 12:31:43 4:31:43 59.60 -122.39 2.9ML 89 km NNE of Fort Nelson

6 2010/08/22 09:30:20 1:30:20 59.53 -122.23 2.4ML 84 km NE of Fort Nelson

5 2010/08/03 20:15:35 12:15:35 59.51 -122.27 2.7ML 81 km NNE of Fort Nelson

4 2010/06/11 22:25:19 14:25:19 59.50 -122.30 3.4ML 79 km NNE of Fort Nelson

3 2009/04/09 16:34:00 8:34:00 59.48 -122.01 2.2ML 83 km NE of Fort Nelson

2 2009/04/08 21:30:23 13:30:23 59.43 -121.92 2.3ML 82 km NE of Fort Nelson

1 2009/04/08 21:27:37 13:27:37 59.46 -122.02 2.3ML 81 km NE of Fort Nelson
6 Investigation of Observed Seismicity in the Horn River Basin 

The Commission began a formal investigation in July 

2011 into the anomalous events recorded by NRCan 

in the Etsho area. The investigation was extended to 

the Tattoo area when similar anomalous events were 

detected there in December 2011. The purposes of the 

investigation were to:

•	 Examine the available evidence to determine if there 

may be a linkage between oil and gas activities and 

the observed events.

•	 Review current research on induced seismicity and 

apply those results to the investigation.

•	 Consider possible mitigation methodologies, where 

appropriate, should a link be established between 

the observed events and oil and gas activities.

The Commission began the investigation with a review of 

hydraulic fracturing and well completion information on 

wells situated near the area of observed seismicity in the 

Etsho area. The dates and times of hydraulic fracturing 

operations were compared to the dates and times of 

recorded seismicity events. 

To obtain additional information to assist in the 

investigation, the Commission issued formal Information 

Requests (IRs) to six operators within the study area. 

The IRs provided the Commission access to data not 

currently required to be submitted by the operators to the 

Commission. Much of this operator information obtained 

Investigation Overview

is proprietary and includes detailed completion statistics, 

microseismic reports, groundwater analyses and seismic 

mapping. In some cases, confidential data is used to 

support findings or analyses but not reproduced within 

the report.

Under British Columbia legislation and regulation, 

specified oil and gas information is required to be 

collected and submitted to the Commission. This 

includes geophysical logs, sample reports and drilling 

and completion information. Data is held confidential for 

a time period as defined in the regulation, dependent on 

well classification.

Through the course of the investigation, the Commission 

consulted with experts from industry, NRCan, the 

University of British Columbia and the Alberta Geological 

Survey. 

A literature search was done as part of the investigation, 

focusing on science and analysis of induced seismicity 

as well as the geology of the Horn River Basin. Included 

in this search were a number of recent public reports on 

induced seismicity incidents in Oklahoma, England and 

Ohio.
Table 2: Richter Scale diagram showing range of magnitudes and effects. Based on US Geological Survey documents.

Event Frequencies courtesy of USGS (estimates).

Magnitude (ML) Description Earthquake Effects Natural Seismicity Occurences Worldwide

 -3.0 – 0.5 Micro-Seismicity

Micro events created when 

hydraulic fracturing breaks rock, 

including micro shear movement 

and tensile fracturing, not felt

Very frequent. Detection reliability extremely 

varied. Frequency estimated at many millions of 

events per year.

 0.5- 2.0 Micro earthquake Very small earthquakes, not felt.

Very frequent. Detection reliability extremely 

varied. Frequency estimated at many millions of 

events per year.

 2.0–2.9 Minor Generally not felt, but recorded.

(Not felt in Horn River Basin) 1,300,000

 3.0–3.9 Minor Often felt, but rarely cause damage. 130,000

 4.0–4.9 Light

Noticeable shaking of indoor items, 

rattling noises. Significant damage 

unlikely.

 

 13,000

Background Information

Measuring Earthquakes

Unless otherwise noted, earthquake 

magnitudes reported in this 

investigation are Richter scale 

magnitudes (ML) (Table 2) and occur 

throughout this report as both positive 

and negative numbers. The Richter 

magnitude scale was originally 

calibrated to a seismograph in 1935. 

At that time, zero on the scale was 

set as an event that would cause 

a one micrometre displacement 

on a seismogram 100 kilometres 

(km) from an epicentre. Instrument 

sensitivity has improved with time 

and modern seismographs are 

capable of detecting earthquakes 

that fall below the original zero value 

set by Richter. Negative Richter 

values account for this enhanced 

sensitivity.

Duration magnitude (Md) used by 

Holland (Holland, 2011) scales 

earthquakes using surface wave 

durations and is consistent with the 

Richter scale.

Investigation of Observed Seismicity in the Horn River Basin 7
8 Investigation of Observed Seismicity in the Horn River Basin 

The locations of earthquakes are generally referred to 

using the terms “epicentre” and “hypocentre” or “focus”. 

The epicentre is the location on the earth’s surface located 

directly above the “hypocentre” or “focus” where an event 

actually occurs underground. 

The CNSN is designed to monitor moderate to strong 

magnitude earthquakes that pose a risk to public safety 

and not to detect low magnitude induced seismicity. 

Currently, the portion of the CNSN for northeast British 

Columbia consists of two stations, the Bull Mountain 

(Hudson’s Hope) and Fort Nelson seismograph stations. 

The limited station coverage in the region results in an 

uncertainty of 5 to 10km in the epicentral locations of 

detected earthquakes. The uncertainty in earthquake 

focal depths is even larger. Minimum magnitude detection 

by CNSN for earthquakes in the northeast BC region is 

estimated at 2.0 ML but in the course of the investigation, 

it was found that the current grid had failed to detect 15 

events greater than 2.0 ML. From June 23 to August 14, 

2011, an operator deployed local seismograph array at 

Etsho detected 19, 2.0 to 3.0 ML events. Only four of these 

events were reported by NRCan. 

Station Coverage of the Canadian 

National Seismograph Network (CNSN)

Induced seismicity may be caused by numerous factors 

including slippage along fault planes, ground subsidence 

from collapse of solution mines and stress release 

from reservoir depletion. Fault movement can occur 

when previously stable subsurface stress conditions 

are altered. Human activities that can alter these stress 

conditions include fluid injection for secondary recovery 

in hydrocarbon reservoirs, injection of waste fluids into 

deep rock formations, withdrawal of hydrocarbons from 

reservoirs and geothermal energy operations involving 

deep fluid injection. 

Fluid injection may trigger induced seismicity. As fluid is 

injected, it flows into the existing pore system of the rock 

and into pre-existing fractures and faults. Across faults 

injection can increase pore pressure, counter-acting 

normal stress across the fault and may act to open an 

existing fault plane. This overcomes friction along the fault 

and can cause fault slippage.

In British Columbia, the only documented case of induced 

seismicity, linked to oil and gas activity, occurred in the 

Eagle Field area, approximately five km north of Fort St. 

John. Twenty-nine Richter magnitude 2.2 to 4.3 events 

were recorded from November 1984 to May 1994. Horner 

(Horner, 1994) used the Davis and Frohlich criteria (Davis 

and Frohlich, 1993) to conclude that the events were 

induced. High pressure fluid injection for secondary oil 

recovery was identified as a possible cause. High volume 

hydraulic fracturing was not employed in the area at that 

time. 

In response to the Eagle Field incident, the regulator 

ordered the injection pressure be lowered. Since that 

time, reservoir waterflood and injection pressures within 

British Columbia are required to be maintained below 

levels capable of re-opening pre-existing fractures or faults. 

This requirement ensures the integrity of confinement 

boundaries and prevents fluid migration beyond the 

targeted formations.

Induced Seismicity in British Columbia
The Horn River Basin in northeast British Columbia lies 

between Fort Nelson and the Northwest Territories border

(Figure 2). Basinal shales of the Horn River Group fill the 

Basin, bounded to the west by the Bovie fault and to the 

east by laterally equivalent Keg River and Slave Point 

Formations reef carbonates (Figure 3). The Muskwa, Otter 

Park and Evie Formations of the Horn River Group are 

highly siliceous, high organic content shale gas targets 

(McPhail et al, 2008). Overlying the Horn River Group are 

over 800 metres (m) of clay rich shales of the Fort Simpson 

Formation (Figure 3). As mineralogy transitions from the 

siliceous shales of the Muskwa Formation to the clay rich 

shales of the overlying Fort Simpson, a natural barrier to 

fracture propagation occurs and the growth of fractures 

caused by hydraulic fracturing is contained to the targeted 

Muskwa and Evie shales.

The Bovie Fault extends over 100 km from the northern 

British Columbia border south and then southwest into the 

foothills. This fault separates the Horn River Basin from 

the Liard Basin (Figure 1). Trending northeast from about 

30 km south of Maxhamish Lake toward the Celibeta High 

is the Trout Lake Fault zone with a strike-slip component. 

(MacLean, Morrow, 2004). 

Figure 2: Provincial map of British Columbia showing locations and 

outlines of Horn River and Liard Basins and Cordova Embayment

Geology of the Horn River Basin

Investigation of Observed Seismicity in the Horn River Basin 9
10 Investigation of Observed Seismicity in the Horn River Basin 

Figure 3: Cross-section of Horn River Basin showing Muskwa, Otter Park and Evie formation shale gas targets. Horizontal wellbores target the Muskwa, Otter Park 

and Evie zones. Diagram modified from Geoscience BC Horn River Basin Subsurface Aquifer Characterization Project schematic cross-section.

Otter Park

metres

100 km

0

1000

West East

LIARD BASIN HORN RIVER BASIN

Debolt/Rundle

Shallow Freshwater Aquifers

Dunvegan

Sikanni

Buckinghorse

Scatter

Chinkeh

Triassic

Mattson

Surface

Figure 1. Schematic stratigraphic cross-section, Horn River Basin and adjacent Liard Basin, modied from Petrel Robertson.

Ft. Simpson Shale

Bovie Fault

Debolt/Rundle

Slave Point /

Keg River

Debolt/Rundle Saline Aquifer

Cretaceous (Buckinghorse) Shale

Muskwa

Evie
Investigation of Observed Seismicity in the Horn River Basin 11

In the Etsho study area, horizontal wells targeting the Horn 

River shales were hydraulically fractured using multiple 

stages of slickwater and sand. The horizontal leg of each 

well was cemented with casing and a “perf and plug” 

technique was used to initiate the fractures, starting at the 

toe of the well and proceeding to the heel. Each hydraulic 

fracture stage was isolated with bridge plugs and received 

multiple perforations prior to pumping the stage. Once all 

the stages were complete, the bridge plugs were drilled out 

and the hydraulic fracture fluid was flowed back to surface. 

Analysis of microseismic data shows that fracture growth 

within the study area is confined to the target Horn River 

shales. It appears that the overlying Ft. Simpson shale 

acts as a highly effective fracture barrier during hydraulic 

fracturing.

Hydraulic fracturing operations in the Etsho area have 

been ongoing from February 2007 to late July 2011. 

During this period, 14 different drilling pads were used to 

drill over 90 wells with more than 1,600 hydraulic fracturing 

stage completion operations (Table 3).

Hydraulic Fracturing in the Horn River Basin Table 3: Pad Hydraulic Fracturing Statistics for Etsho (non-confidential pads). Minimum, maximum and 

average numbers are calculated from all pad data reviewed. Only non-confidential pads are listed in the table.

Well Pad Wells/Pad Stages/

Well

HZ Completed 

(m)

Fluid/Well 

(m3)

Sand/Well 

(Tonnes)

Avg Pump 

Rate (m3/

minute)

Fracs/Pad # of Seismic 

Events

b-100-G 5 5 1,176 11,505 710 12 26 0

c-1-J 9 16 1,837 52,429 3,072 14 147 0

b-76-K 13 15 1,752 58,386 2,454 15 180 1

d-70-J 7 14 1,391 53,800 2,692 15 74 3

d-1-D 7 27 2,727 138,005 5,484 15 176 6

c-34-L 9 18 2,200 63,000 3,200 15 162 7

b-63-K 14 23 2,452 107,738 4,505 14 347 13

Average 8 17 1,846 61,612 3,107 13 149 3

Min. 4 5 1,176 11,505 710 8 26 0

Max. 16 27 2,727 138,005 5,484 15 347 13
12 Investigation of Observed Seismicity in the Horn River Basin 

Recently, two international cases of induced seismicity 

have been documented linking hydraulic fracturing to 

seismic events. In the first case, Dr. C.J. de Pater and Dr. 

S. Baisch (de Pater and Baisch, 2011) directly tie hydraulic 

fracturing in the Bowland Shale near Blackpool, England 

to local seismicity. In the second case, Holland (Holland, 

2011) suggests a relationship between hydraulic fracturing 

in Garvin County, Oklahoma and local seismicity. 

Other studies considered during the investigation include 

Shale Gas Extraction in the UK: A Review of Hydraulic 

Fracturing published by the Royal Academy of Engineering 

in June 2012 and Induced Seismicity Potential in Energy 

Technologies (Pre-Publication) by the US National 

Research Council.

Literature Review

Near Blackpool, England, the Preese Hall–1, spudded Aug. 

16, 2010, targeted gas in the Bowland shale. The Bowland 

shale was encountered at 1,993.3 m (metres) (6,540 feet) 

MD (Measured Depth) and was drilled to 2,744.4 m (9,004 

feet) MD. Hydraulic fracturing ran from 2,337.8-2,727.6 

m (7,670 – 8,949 feet). From March 28 to May 27, 2011 

five hydraulic fracturing (slickwater) stages were run. 

Stage volumes ranged from 596.2–1,669.4 cubic metres 

(m3) (5,000-14,000 bbls) water and 52-117 metric tonnes 

proppant. Bottom-hole pressures reached a gradient of 

21.4 KPa/m (0.95 psi/ft). 

Fifty events, magnitude -2 to 2.3 ML, (generally considered 

to be below the threshold for detection as a “felt” event 

at the surface) were recorded from March 28 to May 28, 

2011. Seismicity is focused around stages 2, 4 and 5. 

Events began early in stage operations and the strongest 

event occurred 10 hours after shut-in. The occurrence of 

events some time after hydraulic fracturing operations is 

interpreted to be the effect of a pressure front spreading 

out from the hydraulic fracturing injection point. De Pater 

and Baisch (de Pater and Baisch, 2011) conclude that 

seismicity magnitude can be mitigated by “rapid fluid flow 

back after the treatments and reducing the treatment 

volume”.

Sufficient movement occurred to deform well casing 

within the target formations on the horizontal leg. The 

casing deformation was attributed to “distributed, small 

magnitudes of bedding plane slip”. 

In Garvin County, Oklahoma, hydraulic fracturing 

operations began at the Picket Unit B Well 4-18 on Jan 17, 

2011. This is a vertical well located in the Eola field at the 

northern edge of the Ardmore basin. The geology of the 

area consists of numerous, major, parallel faults running 

west-northwest to east-southeast. Several northwest to 

southeast trending faults intersect the major faults. The 

Eola field is block faulted and fault dips are near vertical. 

Fifty events, magnitude 1-2.8 Md (Duration Magnitude), 

occurred on Jan. 17-18, 2011. The events began seven 

hours after hydraulic fracture operations started. 

Thirty-nine of the events occurred within 16 hours after 

hydraulic fracturing operations began. Although this 

Blackpool, UK Garvin County, USA

area of Oklahoma has considerable natural seismicity, 

seismological evidence indicates a unique origin different 

from naturally occurring earthquakes.

Holland used the seven question Davis and Frohlich 

criteria (Davis and Frohlich, 1993) to help determine if the 

events were induced. The following summarizes Holland’s 

answers: 

1. Are these events the first known earthquakes of this 

character in the region? (UNKNOWN) It was difficult 

to determine if the events were uniquely different from 

previously recorded earthquakes in the area. 

2. Is there a clear correlation between injection and 

seismicity? (YES) There was a clear correlation between 

hydraulic fracturing and earthquake times.

3. Are the epicenters near wells (within 5 km)? (YES) The 

epicentres are within five kilometres of the Picket well.

4. Do some earthquakes occur at or near injection depths? 

(YES) Most earthquakes occurred near injection depths. 

Depth uncertainty on seismic recording is about 630 m.

5. If not, are there known geologic structures, that may 

channel flow to sites of earthquakes? (YES) Faults exist 

that could channel injection fluid to epicentre locations.

6. Are changes in fluid pressure at well bottoms sufficient 

to encourage seismicity? (YES) Hydraulic fracturing 

pressures are sufficient to encourage seismicity.

7. Are changes in fluid pressure at hypocentral locations 

sufficient to encourage seismicity? (UNKNOWN) Pressure 

diffusion could not be adequately modeled within the Eola 

Field.

Holland concluded that timing and location of the events 

suggested a possible connection to hydraulic fracturing.
Investigation of Observed Seismicity in the Horn River Basin 13

Etsho

 A 20-seismograph dense array was deployed 

in the Etsho area to record, locate and study the 

seismicity in greater detail than possible with 

NRCan data. This array, surrounding the d-1-

D/94-O-8 pad, was operated from June 16 to Aug. 

15, 2011. 

Kiwigana

A second dense array was deployed at Kiwigana, 

40 kilometres to the southwest of the Etsho area 

(Figure 1). This 151-station seismograph array was 

located over the ECA HZ KIWIGANA c-15-D/94-O-7 

multi-well pad and operated from Oct. 25, 2011 to 

Jan. 27, 2012 (Figure 4).

Operator Dense Array Deployments Figure 4: Map of Kiwigana dense array, surrounding c-15-D/94-O-7 pad, showing horizontal wellbores (black lines) and seismograph 

locations (red dots).
14 Investigation of Observed Seismicity in the Horn River Basin 

Induced Seismicity

Hydraulic fracturing is the process of creating cracks 

(fractures), in buried geological formations to create 

pathways along which hydrocarbons trapped within the 

formation can flow into the wellbore at higher rates than 

otherwise possible. The hydrocarbons then flow to the 

surface under controlled conditions through the wellhead 

and are collected for processing and distribution.

During the hydraulic fracturing process, a mixture of water, 

sand and other chemical additives designed to protect the 

integrity of the wellbore and enhance production is pumped 

under high pressure into the formation to create fractures. 

The fractures are kept open by sand or “proppant”, which 

provides pathways to allow the natural gas to flow into the 

wellbore.

As hydraulic fracturing fluids are injected into intact gas 

bearing shales, thousands of micro-seismicity events 

(approx -3.0 to 0.5 ML) are created as the rock is fractured. 

These events are caused by micro shear movement and 

tensile fractures and by the re-opening of existing fractures 

and faults. The micro-seismicity created by fracture 

development is often monitored during hydraulic fracturing 

by a borehole or surface seismograph array to assess the 

effectiveness of the fracture program. Special equipment 

Analysis

is used as these events are far below the detection 

threshold of the seismographic monitoring networks in 

place for earthquake detection. For the purposes of this 

report, the focus is on seismicity that would not normally 

occur when performing hydraulic fracture completions 

(such as seismicity resulting from fault movement). Larger 

magnitude events may occur when fluid injected during 

hydraulic fracturing triggers movement along pre-existing 

stressed faults.

Only one event studied within this investigation was 

reported felt at surface. NRCan’s report on the May 19, 

2011, 3.8 ML event indicates that the event was “felt by 

workers in (the) bush”. No injuries or damage to surface 

structures were reported for this or any of the events 

studied within this investigation.

Twenty-seven of the recorded Etsho events lie within a 

10 km radius circle (Figure 5). Within this same circle are 

seven multi-lateral drilling pads. Five of these pads were 

conducting hydraulic fracturing operations when events 

occurred.
Figure 5: NRCan event locations, event sequence and drilling pad locations, shown within 10km radius red shaded circle.

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Horn River

Basin

094P04

094O02

094O10

094O09 094P12

094O01

094O07

094O08

094P05

4/8/2009

4/9/2009

6/11/2010

8/3/2010

8/22/2010

9/30/2010

9/30/2010

10/3/2010

10/4/2010

10/5/2010

10/5/2010

10/9/2010

10/12/2010

10/12/2010

10/12/2010

3/4/2011 4/7/2011

4/30/2011 4/28/2011

5/3/2011

5/10/2011

5/19/2011

5/19/2011

5/20/2011

5/29/2011

6/26/2011

7/1/2011

7/7/2011

7/14/2011

C- 024-I

B- 025-H

D- 063-H

C- 039-J

B-B077-H

A- 097-J

A-A080-L

A- 069-L

D-N070-K

A- 076-F

A- 016-K

C- 100-G

A-A020-J

C- 089-G

C- 015-G

C-D055-B

D- 071-G

D- 068-H

A- 077-I

A- 027-I

D-A054-A

D- 052-H

A- 012-H

A- 036-A

B- 012-G

B- 045-I

A- 041-A

A- 051-J

D-A052-L

A-A076-F

A- 100-B

D-C087-G

D-A087-G

C- 055-B C-A055-B

B- 086-A

B- 031-A

A- 089-D

B- 060-L

A- 050-C

A-C009-K B- 008-K

A- 006-C

A- 006-J

D- 099-I

A- 027-I

C- 056-E

B-C063-K

D-A090-G

A- 026-G

C-B055-B C-C055-B

C-C001-J

B- 066-I

A- 077-L

C- 062-H

B- 002-H

B-C008-K

A- 051-A

D- 051-A

B- 098-F

C- 067-K

D- 066-F

A-A100-B

B- 090-J

B-D100-G

D-B087-G

C-A016-I B- 016-I

C- 071-A

B- 060-D

C- 035-D

A-A051-A

A- 059-D

D- 069-L

D-I052-L

D-H001-D

C-B063-K

D- 090-G

D- 077-J

D-E087-G

C-E055-B

D- 056-J

D- 085-G

B- 085-A

A- 035-E

B- 048-A

B- 086-K

B- 072-K

A-A097-J

B- 063-B

D-K052-L

D-E052-L

C- 099-K

B-A076-K

C-D063-K

D-J070-J

A- 020-J

D-B077-J

A- 045-G

B-H018-I

B- 077-H

A-E016-I

D- 094-A

C- 093-A

D- 068-D

C- 007-D

D-A063-H

A-A050-C

B-B008-K

C- 094-I

B- 052-I

C-A034-L C-D034-L C-I034-L

D-C052-L

D-G001-D

D-K070-K

D-H070-K B- 076-K B-E063-K

B-A063-K B- 061-K

D-E070-J D-D070-J

A-F020-J

A-D020-J

A- 029-B

C- 018-B

D- 087-G

C-D001-J

B-D018-I

B-C018-I

B-K077-H

B-G077-H

C- 026-A

D-O037-H

D- 054-A

D-A094-A

B- 093-A

D- 039-E

D- 079-D B- 091-B

C- 002-H

A-A009-K

C- 057-D

C-B034-L

C-G034-L

A- 083- D

D-O001-D D-K001-D D-E001-D

D-M070-K

D-D070-K

A- 008-C

A-B077-K

D- 046-K

B-A090-J

D-F070-J

B- 100-G

A-H020-J

B- 018-B

D-G087-G

B- 084-B

C- 001-J

C-A001-J C-E001-J

B- 018-I

B-E077-H

B-N077-H

B-H077-H

D-F037-H D-G037-H

D-J037-H

D-K037-H

D- 025-H

C- 016-I A-C016-I

A- 031-H

C- 021-A

D- 020-D

D- 028-E

A- 027-E

C-A007-D

D- 037-D

122°0'0"W

122°0'0"W

122°15'0"W

122°15'0"W

122°30'0"W

122°30'0"W

59°30'0"N

59°30'0"N

59°15'0"N

59°15'0"N

0 1 2 4 6 Kilometers

Etsho Activity 20 km Buffer

#* Earthquakes

! Major Cities

" Well Surface Hole

( Well Bottom Hole

Well Directional Survey

Earthquakes NEBC

2009 - 2012

1:200,000

!

!

!

!

Kelowna

Victoria

Fort Nelson

Fort St. John

Etsho Area

At Tattoo all seven of the recorded events can be 

encompassed within a 10 km radius circle that 

encloses two multi-well shale gas drilling pads. 

One pad at Tattoo had ongoing hydraulic fracturing 

operations when the seismicity occurred (Figure 6).

Investigation of Observed Seismicity in the Horn River Basin 15
16 Investigation of Observed Seismicity in the Horn River Basin 

Figure 6: Tattoo area NRCan event epicentres and Multi-well Pads, shown within “20km buffer”,

10km radius red circle.

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Northwest

Territories

094O11

094O16

094O14

094O10 094O09

094O15

9/30/2010

9/30/2010

10/4/2010

10/5/2010

10/9/2010

10/12/2010

10/12/2010 5/29/2011 10/12/2010

6/26/2011 7/1/2011

12/8/2011

12/10/2011

12/11/2011

12/11/2011

12/12/2011

12/12/2011

12/13/2011

A- 078-L

B- 095-E

D-A028-F

B-A018-G

B-A055-B

D- 063-H

D- 030-D

C- 092-E A-G098-F

A-A086-B A- 086-B

D- 061-A

A- 076-F

B- 025-L

D- 073-L

D- 077-K

B- 055-B

A- 041-A

B- 066-D

D- 012-L

A-B098-F

C-D068-B

A-B086-B

B- 091-G

B- 058-H

C- 060-D

A-A076-F

B- 018-G

C- 007-J

D- 097-B

C- 015-L

C-B092-E

A- 040-K

A-A098-F A- 098-F

C- 060-G

B-E070-B

B- 077-B

A-C086-B

C- 075-F

D- 058-L

C- 077-L

C- 066-E

A- 025-L

A- 045-E

D-H050-A D-D050-AD-B050-A

C- 062-H

B- 002-H

B-D070-B

C-A068-B

C-E068-B

C- 081-G

D- 013-L

D- 066-F

C- 054-D

C- 053-C

C- 067-L

B- 047-L

A- 035-L

A- 054-L

C- 057-C

B- 057-C

D- 028-F

C-A007-J

A- 069-D

B-A022-L

C- 001-L

A-C001-L

A-C098-F

D-B071-A

D-H071-A D-I071-A

D- 070-F

B- 096-E

C-A057-C

D- 069-C

D-B028-F

B- 048-A

B- 022-L

A-B001-L

C- 030-K

C- 020-K

C- 049-E

B- 059-E

C- 099-D

A- 027-L

C- 035-E

A- 002-D

B- 066-B

D-A063-H

C- 012-L

B- 021-L

A- 001-L

C- 081-D

A- 056-F

B- 070-B

A- 033-L

A- 028-D

C- 066-L

D- 076-E

B- 044-L

C- 063-L

C- 042-C D-C050-A

D-I050-A

B- 091-B

D-J050-A

C- 002-H

C- 029-D

B- 057-L

C- 083-L

C-A092-E

A- 021-L

A-A001-L

A-D001-L

D- 028-J

C- 027-J

C-C068-B C-B068-B

D-A068-B B- 063-B C- 056-A

D- 071-A D-A071-A

D-D071-A

C- 057-D

A- 083-D

B

o

vie

L

a

k

e

F

a

ult

Trout Lake

Fault Zone

122°15'0"W

122°30'0"W

122°30'0"W

122°45'0"W

122°45'0"W

123°0'0"W

60°0'0"N

59°45'0"N

59°45'0"N

Tattoo Field

0 1 2 4 6 Kilometers

Tattoo Activity 20 km Buffer

#* Earthquakes

! Major Cities

" Well Surface Hole

( Well Bottom Hole

Well Directional Survey

Earthquakes NEBC

2009 - 2012

1:200,000

!

!

!

!

Kelowna

Victoria

Fort Nelson

Fort St. John

Tattoo Area

Horn River

Basin

Seismicity Event Locations and Depth – Proximity to Hydraulic 

Fracturing

A number of events, ranging from magnitude -0.8 to 

3.0 ML, were recorded by the Etsho dense array during 

hydraulic fracturing. Of these, 216 are interpreted to be 

related to fault movement (197 events, magnitude 1.0 – 

2.0ML and 19 events magnitude 2.0-3.0 ML). Operator 

provided b-value analysis indicated that magnitudes from 

0.5ML to 1.0ML indicate the transition from fracture driven 

seismicity to seismicity driven by fault movement. For the 

dense array’s operational date range, June 23 to August 

14, the two northeast B.C. stations in the CNSN recorded 

four events (mag. 2.5 to 3.1 ML). 

Figure 7 shows the horizontal wellbores for the d-1-D 

drilling pad, volumes injected at each hydraulic fracturing 

stage and the magnitude >1.0ML events occurring from 

June 23 to August 14, 2011. 
Investigation of Observed Seismicity in the Horn River Basin 17

Figure 7: Diagram showing d-1-D wellbores and events >1.0. Wellbores are black 

lines and stages with relative injection volumes are thickened blue sections.

The horizontal and vertical locations of 

several events at Etsho detected by NRCan 

were relocated by the operator using data 

obtained from the dense array. The results 

of this work placed event hypocentres within 

200 m, vertically and horizontally, of hydraulic 

fracturing stages. In cases where events 

could be confidently linked to hydraulic 

fracturing stages, events occurred during the 

event stage or prior to the following stage 

beginning. Associated faults, identified on 

microseismic plots as linear swarms, could 

be seen intersecting stage locations. True 

vertical depths (TVD) of hydraulic fracturing 

completions at the Etsho d-1-D pad range 

from approximately 2,650 to 2,889 metres 

TVD. Of the 69 magnitude 1.5 to 3.0 ML

seismic events recorded by the dense array 

and linked to this pad, all fall within the 

targeted formations. Sixty-six of these events 

occur between 2,800 and 2,870 metres.

At Kiwigana, numerous micro-seismicity 

events, ranging from -1.7 to 0.5 ML, were 

detected between Oct. 25, 2011 and Jan. 27, 

2012 by the operator deployed dense array. 

These micro-seismicity events resulted from 

tensile failure and shear movement during 

the normal process of hydraulic fracturing to 

develop the reservoir. An additional 18 events 

ranging from 1.0 to 1.86 ML were detected 

and are interpreted to be the result of injection 

fluids triggering movement along pre-existing 

faults. 

Figure 8 is a cumulative microseismic plot 

showing a vertical profile of the Kiwigana 

wellbores at the c-15-D pad. Coloured dots 

indicating micro-seismicity show that hydraulic 

fracturing operations are successfully 

contained to the Horn River shale target 

horizons and that the overlying Ft. Simpson 

shale provides an effective barrier to vertical 

fracture growth. A fault is suggested near 

the centre of the wellbores by the downward 

trending collection of microseismic points.
18 Investigation of Observed Seismicity in the Horn River Basin 

Figure 8: Cumulative microseismic plot for Kiwigana, coloured dots indicate contained micro-seismicity events caused by tensile and shear failure of intact 

shale. Trail of coloured dots suggest reopening or movement of pre-existing fault. Generalized stratigraphic column to right.
Investigation of Observed Seismicity in the Horn River Basin 19

Hydraulic Fracturing Timing vs. Seismicity Event Timing

Hydraulic fracturing dates and times were compared to seismicity event times (Figure 9). At Etsho and Tattoo, all 38 NRCan reported events occurred either during a hydraulic fracturing 

stage or sometime after one stage ended and another began. No events were recorded before hydraulic fracturing operations began or after the last hydraulic fracturing operations ended. 

Figure 9: Timing of NRCan reported Events (black dots) vs. Magnitude. Timing of hydraulic fracturing operations (coloured columns).

c-68-B/94-O-15 c-34-L/94-O-8 

b-76-K/94-O-8 

c-1-J/94-O-8 d-87-G/94-O-8 

c-55-B/94-O-9 

4

3

2

1

1.5

0.5

2.5

3.5

2008 2009 2010 2011

Jan 

Ootla 70-J 76-K 

NRCan-Reported Earthquake Events (Richter Scale) 

Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 

d-70-J/94-O-8 

Seismic Event 

Correlations of Event Times to Horn River Pad Operations

d-70-K/94-O-8 

d-52-L/94-O-8 b-18-I/94-O-8 

b-63-K/94-O-8 

d-1-D/94-O-9 
20 Investigation of Observed Seismicity in the Horn River Basin 

Hydraulic fracturing and NRCan event timing were compared at 15 Etsho and Tattoo drilling pad sites. Nine pads had ongoing hydraulic fracturing operations when the NRCan 

events occurred (Figure 9). The other multi-well drilling pads in the Etsho area could not be linked to the NRCan events by location or timing.

Eighteen magnitude 1.9 to 3.0 ML events were selected from dense array microseismic plots. These events were selected because they were located adjacent to hydraulic fracturing 

stages and could be connected to a single stage fluid injection with some confidence. Evidence strongly suggests that all events were triggered by fluid injection at adjacent stages. 

Figure 10 shows the time lapse from the beginning of the selected stage to the seismicity event time. One stage was linked to 3 events, four stages to 2 events each and 7 stages 

had one event. On average, stage start time to stop time was 5 1⁄2 hours. Eight events occurred during stage operations. Seventeen events occurred within 17 1⁄2 hours and all 

events had occurred within 24 hours of assigned stage start times.

All stages along the d-G1-D (southwestern most) wellbore had 10,000 m3 total hydraulic fracturing fluid placed. For these stages, two injections of 5,000 m3 were placed at the same 

stage interval separated by about one hour. Eight of the events connected to the 11 stages graphed with 10,000 m3 total fluid placed, occurred prior to the second injection of 

5,000 m3. 

Figure 10: Timing of seismicity events, resulting from fluid injection at selected hydraulic fracturing stages. Green dots designate events linked to stages with 10,000 m3 total ‘Fracturing Fluid Placed’ 

(two injections of 5000 m3 separated by one hour). Red dots are events linked to stages with 5,000 m3 total ‘Fracturing Fluid Placed’.

Horn River Pad Operations d-1-D Pad

Time Lapse from Start of Hydraulic Fracturing to Associated Seismic Event

0 60 120 180 240 300 360 420 480 540 600 660 720 780 840 900 960 1020 1080 1140 1200 1260 1320 1380 1440

1.0

1.5

0.5

2.5

3.5

2.0

3.0

4.0

Richter 

Scale

Magnitude

Minutes (12 hrs) (24 hrs)

Start of Hydraulic Fracturing Operation

330 Mins (5.5 hrs): Average Duration of Hydraulic Fracturing Stage

Minutes to Seismic Events 

Mag 2.14 145 mins

Mag 2.01 9 mins

Mag 2.66 146 mins

Mag 2.55 49 mins

Mag 2.70 108 mins

Mag 1.97 110 mins

Mag 2.29 179 mins

Mag 2.50 333 mins

Mag 2.09 273 mins

Mag 2.54 660 mins

Mag 2.17 681 mins

Mag 2.02 409 mins

Mag 3.04 962 mins

Mag 1.94 1043 mins

Mag 2.42 751 mins

Mag 2.02 877 mins

Mag 1.91 707 mins

Mag 2.60 1408 mins 

10,000 m3

5,000 m3

Frac Fluid Placed
Investigation of Observed Seismicity in the Horn River Basin 21

Proximity to pre-existing faults, injection volumes, 

breakdown pressures and hydraulic fracture pump rates 

were examined as possible controls on seismicity.

 

Dense array data was used by an operator to compare 

pumping rates and fault proximity to seismicity frequency 

and magnitude at the d-1-D pad. The operator study 

concluded that seismicity was greatest near pre-existing 

faults and subsided away from the mapped fault fairway. 

As hydraulic fracturing proceeded from toe to heel along 

horizontal wellbores, seismicity magnitude increased 

as wellbore stages encountered micro-seismically 

visible faults. Higher magnitude events, caused by fault 

movement, declined or fell off completely as completion 

stages moved away from faulting. According to the 

operator study, as hydraulic fracturing stages continued 

along the horizontal legs and pump power was reduced, 

events became less frequent. This indicates either 

no faults were being intersected or additional faults 

encountered were not critically stressed or injection was 

insufficient to trigger fault movement. The operator analysis 

concluded that proximity to faulting appeared to have a 

greater effect on seismicity than pump rates. 

Faulting was identified on microseismic plots and 3-D 

seismic supported fault mapping provided by operators. 

In only one case did a linear seismicity swarm clearly 

Controls on Seismicity

coincide with a 3-D seismic mapped fault. A much larger 

linear swarm of events mapped at d-1-D, interpreted 

to be occurring along a single reactivated fault, had no 

supporting 3-D mapped faulting. Microseismic plots were 

not available for the May 19, 2011 3.8 ML event. The 

maximum event verified by dense array and visible on 

microseismic plot was the July 7, 2011, 3.1 ML (NRCan) 

event located within the large linear swarm at d-1-D 

(figure 7). 

At Etsho, an operator analysis showed a slight correlation 

between hydraulic fracture pumping rates and event 

magnitude and frequency. Pump rates were reduced 

from16 m3/min to 13 m3/min on July 19, 2011. In this 

operator analysis, after the July 19 pump rate reduction, 

the frequency of higher magnitude events decreased.

Figure 11 shows the results of a Commission analysis. 

Event magnitudes, collected from the dense array, 

from June 23 to July 31 are compared to pump rates, 

breakdown pressures and injection volumes for the 

corresponding period. Magnitudes are averages of all 

events occurring on the date. Pump rates, pressures and 

volumes were averaged by date for all the wells on the 

d-1-D/94-O-8 pad. The magnitude drop around July 9 

(Figure 11) indicates a decline in magnitude as hydraulic 

fracturing stages moved away from pre-existing faults 

that became active as a result of fluid injection. Although 

pump rates were below average from July 15–20, no 

corresponding decline in magnitudes is seen in this 

analysis. Some periods of direct relationship can be seen 

between breakdown pressures and magnitudes. As 

stated previously, magnitudes decline around July 9 as 

completions move away from the active faulted interval. 

Magnitudes after July 9 suggest few events past that date 

are related to fault movement. 

Within the active faulted zone (June 23 to July 9) 

magnitudes show some correlation to breakdown 

pressures. 
22 Investigation of Observed Seismicity in the Horn River Basin 

Figure 11: Change in average magnitude with changes in daily fracture 

volume, pump rate and breakdown pressure over time. Frac fluid placed, 

pump rates and breakdown pressures are daily averages taken from 

d-1-D pad completions report. Magnitudes are also daily averages.

Hydraulic fracturing pump rates at Kiwigana were maintained 

at slightly below 13 m3/min. Micro-seismicity frequency and 

magnitude were fairly consistent during the Oct. 2011 to Jan. 2012 

hydraulic fracturing operations, with magnitudes ranging from -1.7 

to 1.9 ML. 

Eighteen events were above 1.0 ML for a period from Nov. 6-10, 

2011 suggesting minor fault movement. A review of microseismic 

plots for this time period shows that as the initial hydraulic 

fracturing stages were completed in the c-A15-D wellbore, a 

trailing swarm of microseismic points, indicating fault slippage, 

extended below and to the southwest of the completion interval 

and stage location. Here again, fluid injection at a fracturing 

stage while proximal to a critically-stressed fault appears to trigger 

seismicity. 

At Kiwigana, a consistent, relatively low pump rate may have been 

effective in mitigating seismicity magnitude and frequency. Only 18 

events were interpreted to be the result of fault movement. None 

of these very low magnitude events were detected by NRCan or 

felt at surface.

2011 Horn River Pad Operations d-1-D Pad

Breakdown Pressure versus Average Magnitude

June July

32

48

46

42

44

50

40

36

38

34

23 24 25 26 27 28 29 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 

Breakdown 

Pressure

(MPa)

Average

Magnitude

 (ML)

0.8

-0.4

-0.2

0.0

0.2

-0.6

0.4

1.0

0.6

Pump Rate versus Average Magnitude

June July

0

16

14

10

12

18

8

4

6

2

23 24 25 26 27 28 29 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 

Pump Rate

(m3

/min) Average

Magnitude

 (ML)

0.8

-0.4

-0.2

0.0

0.2

-0.6

0.4

1.0

0.6

Frac Fluid Placed versus Average Magnitude

June July

3250

5250

5000

4500

4750

5500

4250

3750

4000

3500

23 24 25 26 27 28 29 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 

Frac Fluid 

Placed

(m3

)

Average

Magnitude

 (ML)

0.8

-0.4

-0.2

0.0

0.2

-0.6

0.4

1.0

0.6
Investigation of Observed Seismicity in the Horn River Basin 23

The Davis and Frohlich induced seismicity criteria (Davis 

and Frohlich 1993) is a generally accepted methodology 

for the identification of induced seismicity. These criteria 

strongly suggest the Horn River Basin seismicity was 

induced by hydraulic fracturing.

Davis and Frohlich Criteria – related to Horn River Basin

1. Timing

a. Are these events the first known earthquakes of this 

character in the region? Probably, only some mag >2.5ML

events would have been detected in the Horn River Basin 

back to 1999. Prior to 1999, magnitude 4.0ML events 

would have been detected as far back as the 1960’s. No 

events were recorded by NRCan in the Horn River Basin 

prior to April 2009

b. Did the events only begin after hydraulic fracturing 

had commenced? Yes, all the Horn River Basin events, 

recorded by both NRCan and the operator deployed dense 

array, began after hydraulic fracturing commenced.

c. Is there a clear correlation between hydraulic fracturing 

and seismicity? Yes, all the seismic events in Horn River 

Basin occurred during or between hydraulic fracturing 

stages.

Davis and Frohlich Criteria

2. Location

a. Are epicenters within five kilometres of wells? Yes, all 

epicentres occurred within five kilometres of hydraulic 

fracturing operations.

b. Do some earthquakes occur at or near hydraulic 

fracturing depths? Yes, the dense array report shows 

seismicity occurring within 300 metres of hydraulic 

fracturing stages.

c. Do epicenters appear spatially related to the production 

region? Yes, all the NRCan reported events were located 

within five kilometres of hydraulic fracturing operations in 

the Horn River Basin. Dense array hypocentres locate the 

events within 1 km.

3. Fluid pressures, etc.

a. Did hydraulic fracturing cause a significant change in 

fluid pressures? Yes, hydraulic fracturing must increase 

localized pressures to breakdown pressure in order to 

fracture the reservoir rock. This pressure is greater than 

original formation pore pressure. 

b. Did seismicity begin only after the fluid pressures had 

increased significantly? Yes, the events occurred after 

hydraulic fracturing commenced and fluid pressures had 

increased significantly.

c. Is the observed seismicity explainable in terms of current 

models relating hydraulic fracturing to fault activity? Yes, 

current induced seismicity models relate increased pore 

pressure from fluid injection to overcoming friction along a 

fault resulting in fault slippage. 

Horizontal portions of wellbores at Etsho are roughly 2500 

to 3000 metres long. Five of the six operators covered 

by the Information Request reported no wellbore integrity 

issues in 91 of the 93 wellbores at Etsho. Two instances 

of wellbore deformation along horizontal sections were 

reported by one operator. These occurred over a short 

interval beginning at 3,011 m KB (Kelly Bushing) in the 

d-A1-D/94-O-9 well. In this instance, casing deformation 

was minor and did not hinder completion operations. At 

d-1-D/94-O-9, the deformation was encountered at 4,245 

m KB and the casing distortion blocked completion efforts 

at 4,288 m KB. Neither incident posed any risk with respect 

to safety, containment or fluid migration.

The operator reported that the deformation occurred in the 

horizontal section of the wellbores only and no wellbore 

issues were reported in the vertical sections of any wells. 

This deformation was detected in July 2011. Hydraulic 

fracturing stages for the two affected wellbore measured 

depths were completed from June 16 to July 3, 2011. 

All geophysical logs, containing wellbore caliper and 

image data, were run in Sept. and Oct. 2010, prior to the 

deformation occurring. 

The bit (117.5mm) used to drill out the stage packers is 

very close to the inside diameter of the casing (121.0mm)

and would have detected any vertical wellbore casing 

distortion. As a result of not encountering any further 

distortion, no subsequent casing or cement evaluation 

tools were run. 

Wellbore Integrity
24 Investigation of Observed Seismicity in the Horn River Basin 

All Etsho operators conducted two and three dimensional 

seismic surveys and interpreted faulting before conducting 

hydraulic fracturing operations. 

Fault mapping at Etsho shows abundant faulting. Interpretations 

vary but it appears most of this faulting (including the larger, 

regional faults in this grouping) is deep seated and concentrated 

in a north-south trending fault fairway centered at Etsho. Minor, 

secondary faulting is evident, generally trending northwest to 

southeast, at approximately 45 degrees.

From the data reviewed, faulting appears to be confined below 

the lower Fort Simpson shale extending into the basement 

(Precambrian) or within the shallower Debolt Formation. 

No faulting was seen to extend through the Fort Simpson 

Formation and no evidence was found that Middle Devonian 

aged faulting, in this area, could provide a conduit for fluids to 

zones above the Fort Simpson shale.

Faults were also interpreted from available microseismic plots. 

In the case of the dense array at Etsho, daily microseismic 

plots (June 16 – July 31, 2011) that showed high magnitude 

events were submitted for the investigation. Along with higher 

magnitude seismicity, dates and the stages hydraulically 

fractured for that date were highlighted. Event dates could 

be compared to the plots and fault mapping. In all cases 

examined, faulting could be seen on the plots as linear swarms 

or a smaller bundle of events with a large signature event 

represented by a large dot. Faults can also be seen as long, 

trailing legs of dots on microseismic vertical profiles (Figure 

12). In this case, hydraulic fracturing fluids or a pressure 

front appear to have migrated along the fault creating microseismicity events that reach the underlying Keg River formation. 

Pre-Existing Faults Figure 12: Micro-seismicity events (coloured circles) and hydraulic fracture stages (green ellipses) along horizontal wellbore legs.
1.	 The seismicity observed and reported by NRCan 

in the Horn River Basin between April 2009 and 

December 2011 was induced by fault movement 

resulting from injection of fluids during hydraulic 

fracturing.

2.	 No injuries or property damage were reported as a 

result of the induced seismicity. Only one event was 

reported by NRCan to have been felt at the ground 

surface.

3.	 The fractures developed during the hydraulic 

fracturing operations studied within the investigation 

were effectively confined to the target Horn River 

shales by the overlying Ft. Simpson shales. No 

effects on shallow aquifers or the environment were 

identified.

4.	 The magnitude and frequency of the induced 

seismicity investigated by the Commission may be 

influenced by numerous factors including pump rate, 

breakdown pressure and proximity to pre-existing 

faults. 

Findings

5.	 No casing deformation was reported in the vertical 

portion of wellbores and no reservoir containment 

issues were identified. Minor casing deformation 

within the horizontal well portion of target shale 

formations occurred in 2 instances. The cause of the 

casing deformation could not be conclusively linked to 

the seismicity. 

6.	 Fault mapping provided by operators shows abundant 

sub parallel north-south trending faulting through the 

Etsho and Tattoo areas. These faults are generally 

deep seated and do not show displacement above 

the Ft. Simpson shale. The Ft. Simpson shale is 

considered to be a ductile fracture barrier. Fault 

reactivation in this structural setting is not considered 

a threat to shallow overlying aquifers. 

7.	 Seismograph station additions are needed to the 

CNSN to improve monitoring for induced seismicity in 

northeast British Columbia.

Investigation of Observed Seismicity in the Horn River Basin 25
26 Investigation of Observed Seismicity in the Horn River Basin 

1.Improve the accuracy of the Canadian National Seismograph 

Network in northeast B.C.

During the investigation it became evident that the existing 

coverage of the CNSN, operated by NRCan for northeast 

B.C. is adequate for large conventional earthquake 

detection but could not reliably provide the spatial accuracy 

necessary to positively identify smaller seismic events 

associated with induced seismicity. The current grid did 

not detect 15 magnitude 2.0 to 3.0 ML events which were 

detected by the more accurate dense array temporarily 

installed at Etsho. 

The Commission has been working with NRCan and 

the Alberta Geological Survey to determine what 

enhancements to the existing detection grid are needed 

to provide accurate and timely identification of induced 

seismicity.

Action: Geoscience BC has organized funding for a 

five year project to install and operate six additional 

seismograph stations for the CNSN. NRCan has 

completed site surveys and installation is scheduled for 

late 2012. The enhanced grid will reliably identify induced 

seismicity, providing detection sensitivities below 2.0 ML

and surface location accuracy to within one kilometre. 

Recommendations

2. Perform geological and seismic assessments to identify preexisting faulting.

While several faults were believed to have been 

intersected by wellbores at Etsho, only a few of these 

faults slipped resulting in seismicity. In one case a mapped 

fault coincided with a microseismic plot event swarm. In 

other areas, seismicity occurred where faults had not 

been mapped. It currently cannot be determined which 

intersected fault will move or what injection pressure 

or volume will trigger the event. Operators do identify 

as many pre-existing faults as practical and can tailor 

their hydraulic fracture programs to include enhanced 

monitoring for seismicity when completing near these faults

Action: Operators should review geological and seismic 

data to identify pre-existing faulting. If induced seismicity 

is detected, the active fault could be located and avoided 

in subsequent wellbores. Additional mitigation procedures, 

such as bypassing stages adjacent to a known active fault 

might also be considered. Monitoring for events will be 

done by the Commission under Recommendation 3.

3. Establish induced seismicity monitoring and reporting 

Procedures and Requirements.

A notification and consultation procedure provides a means 

for the Commission to respond to induced seismicity in 

northeast B.C. If seismicity is detected on the CNSN or 

an operator deployed dense array, the Commission would 

contact the operator to investigate the occurrences and 

determine appropriate mitigation options when required. 

Action: Each case will require a unique response. 

Incidents will be evaluated on the basis of event frequency, 

magnitude, ground motion, depth and proximity to 

populated areas. In the case of the Horn River Basin area, 

the Commission will commence consultations regarding 

additional monitoring requirements or mitigation as soon as 

induced seismicity is detected. 

Specific to the Horn River Basin, with the additions to the 

CNSN, induced events should be reliably and consistently 

detected and reported at magnitude 2.0 ML . Mitigation 

discussions with the operator will begin immediately. 

Mitigation steps taken will vary dependent on the risk 

posed by the events and may include enhanced data 

recovery for research purposes. 

An order to suspend hydraulic fracturing specific to the 

well under completion could be issued dependent on 

an evaluation of the previously stated criteria of event 

frequency, magnitude, ground motion, depth and proximity 

to populated areas. Operators will immediately suspend 

hydraulic fracturing operations for a well upon detection of 

a 4.0 ML or greater event.

4. Station ground motion sensors near selected NEBC 

communities to quantify risk from ground motion. 

Along with location and depth, it is important to know how 

much the ground actually moved at a given location during 

a seismic event. Ground motion sensors record ground 

acceleration and enable a correlation between magnitude 
Investigation of Observed Seismicity in the Horn River Basin 27

and ground acceleration. This has implications for human 

safety and infrastructure integrity.

Action: NRCan experts will be consulted to determine 

equipment selection, location, installation and operation of 

ground motion sensor stations.

5. The Commission will study the deployment of a portable 

dense seismograph array to selected locations where induced 

seismicity is anticipated or has occurred.

A dense array, separate from the regional grid, is 

necessary to determine event depth, a key to diagnosing 

induced seismicity. Depth is required to fully understand 

the range of fault movement and risk to shallow aquifers. 

Focal mechanism determination, improved location 

resolution and lower magnitude detection are also possible 

benefits of a dense array. They can be designed to be 

quickly deployable, placed on the ground, and may require 

as few as five seismographs.

Action: Two operators have deployed three dense arrays 

in the Horn River Basin and an additional research dense 

array is being considered by NRCan for the Basin. The 

Commission will seek funding for a portable dense array 

to be deployed as needed for induced seismicity research 

and data collection.

6. Require the submission of micro-seismic reports to monitor 

hydraulic fracturing for containment of micro fracturing and to 

identify existing faults. 

Microseismic data can identify geological features such 

as faults where there may be increased risk of inducing 

seismicity beyond magnitude 2.0 ML. In addition, 

microseismic plots can verify that hydraulic fracturing is 

confined to the target zone by outlining both the vertical 

and lateral extent of the fracturing. 

Action: The Commission will develop requirements for 

submission of information gathered from microseismic 

monitoring during hydraulic fracturing. Data gathered will 

be limited to that which is necessary to show fracture 

containment and faulting. The format shall be determined 

in consultation with stakeholders including other regulators 

outside of British Columbia. Consideration of the 

proprietary nature of microseismic data must be included in 

the development of submission requirements.

7. Study the relationship between hydraulic fracturing 

parameters and seismicity.

At Etsho and Kiwigana magnitudes may have declined as 

pump rates were reduced or held low. This investigation 

found weak correlations between pump rates and 

magnitude and breakdown pressure and magnitude. The 

historical response to induced seismicity from fluid injection 

has been to either stop operations or reduce injection 

rates. Seismicity frequency at the Rangely oilfield in 

Colorado (Gibbs et al, 1972) directly corresponded to the 

amount of water injected per year.

Action: The Commission is continuing its analysis of 

hydraulic fracturing data to attempt to find correlations 

between hydraulic fracturing parameters and event 

magnitude. Reducing pump rates or injection volumes will 

be considered if induced seismicity is detected beyond the 

criteria set out under recommendation three.
28 Investigation of Observed Seismicity in the Horn River Basin 

Horn River Basin seismicity events, from 2009 to late 2011, 

were caused by fluid injection during hydraulic fracturing. 

All events occurred during or between hydraulic fracturing 

stage operations. Dense array data accurately placed the 

depth and location of events at or near hydraulic fracturing 

stages. Only one event was reported as “felt” and no 

events were felt beyond 10 km of the epicentres.

Faulting transecting horizontal wellbores can be identified 

on microseismic plots. Some events greater than 2.0 ML

were located at the intersection of faults and wellbores 

when adjacent hydraulic fracturing stages were being 

completed. In other circumstances, faults intersected 

wellbores yet no anomalous events were detected. Fault 

movement is dependent on numerous factors such as insitu stress and there is no reliable method to identify which 

faults will slip or under what conditions. Further research 

is needed to determine if induced seismicity from hydraulic 

fracturing can be controlled by either altering hydraulic 

fracturing parameters or by fault characterization and 

avoidance.

The current coverage of the CNSN was designed as part 

of a national large earthquake preparedness system and is 

inadequate for the reliable detection of induced seismicity. 

Only four of the 19 (2.0 to 3.0 ML) events detected by the 

dense array at Etsho between June 23 and Aug. 15, 2011 

were detected by the current regional grid. Recommended 

Conclusion

improvements to the CNSN will improve location resolution 

to within one km and magnitude detection to <2.0 ML. 

Site surveys for the additional seismograph stations being 

added to the CNSN have been completed. Installation 

of the new stations is tentatively scheduled for late 2012. 

Dense arrays will be deployed where appropriate to 

determine event depth and precise location. 

None of the events under investigation resulted in any 

injury or property damage and only 1 event was recorded 

by NRCan as having been “felt” at the surface. The 

recommended ground motion sensors will accurately 

record any ground acceleration from future events. This 

enables a correlation between magnitude and any ground 

motion and eliminates the need to rely on ‘felt’ reports to 

gauge possible effects at surface.

Recommended improvements to the CNSN and 

implementation of a notification and consultation procedure 

will provide the necessary early detection and mitigation 

action as well as for additional research on mitigation 

methods. It is essential to take pre-emptive steps to 

ensure future events are detected and the regulatory 

framework adequately provides for the monitoring, 

reporting and mitigation of all seismicity related to hydraulic 

fracturing thereby ensuring the continued safe and 

environmentally responsible development of shale gas 

within British Columbia.
Davis, S.D. and Frohlich, C., 1993. Did (or will) fluid 

injection cause earthquakes? – Criteria for a Rational 

Assessment, Seismol. Res. Lett. 64(3-4), 207-224

De Pater, C.J. and Baisch, S., 2011 Geomechanical 

Study of Bowland Shale Seismicity, Synthesis Report 

commissioned by Cuadrilla Resources Ltd.

Gibbs, J., Healy, J., Raleigh, C., Coakley, J. 1972 

Earthquakes in the Oil Field at Rangely, Colorado, U.S. 

Geological Survey, Open File Report 72-130

Holland, Austin, 2011, “Examination of Possibly Induced 

Seismicity from Hydraulic Fracturing in the Eola Field, 

Garvin County, Oklahoma”, Oklahoma Geological Survey 

Open File Report OF1, 2011.

Horner, R.B., Barclay, J.E. and MacRae, J.M. ,1994, 

Earthquakes and Hydrocarbon Production in the Fort St. 

John Area of Northeastern British Columbia, Canadian 

Journal of Exploration Geophysics, Vol. 30, No. 1, (June 

1994), P. 38-50

References

MacLean, B.C., Morrow, D.W., 2004, Bulletin of Canadian 

Petroleum Geology, Vol. 52, No. 4 (December 2004, P. 

302-324

McPhail, S., Walsh, W., Lee, C., Monahan, P.A., 2008, 

British Columbia Energy and Mines, Open File, Report # 

2008-1

Nicholson, C. and R.L. Wesson, 1990, Earthquake Hazard 

Associated With Deep Well Injection – A Report to the U.S. 

Environmental Protection Agency, U.S. Geol. Surv. Bull, 

1951.

Hayes, B.J., 2010, HORN RIVER BASIN Subsurface 

Aquifer Characterication Project, Presentation to 

Unconventional Gas Technical Forum, Geoscience BC 

project

Investigation of Observed Seismicity in the Horn River Basin 29