A Review of Seismicity in Southwest Western Australia for 24 Months from July 2022 to June 2024

Abstract

The wheatbelt region of southwest Western Australia is an area of elevated intraplate seismicity. The seismicity is highly clustered, with 80 active clusters identified over the last 20 years. This report reviews the seismicity between July 2022 and June 2024, which includes continuing seismicity from the Arthur River region, and a damaging magnitude 5.0 event near Gnowangerup. Most of the seismicity in this period occurs in 21 clusters; 10 were previously active and 11 are new. Of interest is the contemporaneous seismicity of 5 neighbouring cluster pairs, suggesting a possible causative link.

Full text

Australian Earthquake Engineering Society
2024 National Conference, 21 – 23 November
Adelaide, South Australia
AEES 2024 Conference, Nov 21 – 23 1
A Review of Seismicity in Southwest Western Australia
for 24 Months from July 2022 to June 2024
V.F. Dent1 & C.D.N. Collins2
1. Honorary Research Associate, The UWA Institute of Agriculture, UWA, Perth:vic_dent@yahoo.com
2. GPO Box 2972, Canberra, 2601; Email: collins@pcug.org.au
Abstract
The wheatbelt region of southwest Western Australia is an area of elevated intraplate seismicity. The
seismicity is highly clustered, with 80 active clusters identified over the last 20 years. This report
reviews the seismicity between July 2022 and June 2024, which includes continuing seismicity from
the Arthur River region, and a damaging magnitude 5.0 event near Gnowangerup. Most of the
seismicity in this period occurs in 21 clusters; 10 were previously active and 11 are new. Of interest is
the contemporaneous seismicity of 5 neighbouring cluster pairs, suggesting a possible causative link.
Keywords: Seismicity, Southwest Western Australia, Clusters
1 Introduction
The wheatbelt region of southwest
Western Australia (SWA) is a region of
elevated intraplate seismicity, and
commonly known as “The southwest
seismic zone” (SWSZ) of Western
Australia, a term coined by Doyle (1971)
when reviewing earlier work by
Everingham (e.g. Everingham 1968).
Denham et al. (1987) noted that the
seismicity in this region is highly
clustered with events occurring in
groups confined within a small area.
However, this observation was not
elaborated on for the following 20 years.
Following initial reviews of cluster
groupings in SWA and elsewhere by
Dent (2008a, 2012), a study was
commenced to identify and name
cluster locations. Leonard (2008)
suggested a “South West Australia
Region” of enhanced seismicity – one of
Figure 1. Location map. Earthquake Zones of Dent (2014;
2017). Earthquakes from July 2022 to June 2023 inclusive.

AEES 2024 Conference, Nov 21-23 2
four such regions in Australia for which he discussed the seismicity. Leonard’s South West Australia
region was divided by Dent (2014) into 8 latitudinally-based sub-zones, and later revised (Dent 2017)
to the 10-zone configuration shown in Figure 1. The seismicity of SWA between July 2012 and June
2022 has been analysed from a “clustered” viewpoint in 8 previous reports by Dent and co-workers
(eg. Dent & Collins, 2018; Dent & Love, 2022). Seventy-five cluster locations had been proposed by
the end of 2022 (70 clusters listed in Dent, (2021), and a further 5 in Dent & Collins, (2022)). They have
been named according to the name of the zone within which they fall.
Clusters can be categorised as either “MainShock/Aftershock” sequences (MSAS), or “swarm-like”,
where there is frequently no “principal event”. Seismicity in SWA is mainly of the latter variety, and
where an event, or group of events is considered to be of the former category, it is not assigned a
cluster location. However, the distinction between categories can become difficult and debatable at
times.
In this report, earthquakes and groups of earthquakes are considered; most are assigned to previously
identified cluster locations but some locations are new. The predominant source of events during the
period studied here was a small region about 10 km SW of Arthur River. This sequence started with
an ML 4.0 event on 8 January 2022, followed by an ML 4.8 event on 26 January 2022 (Murdie et al.,
2022, Dent & Love, 2022).
2 Earthquake Locations
Most earthquake locations are derived by Geoscience Australia (GA), and they usually have
uncertainties quoted of about +/- 5-10 km. Most of the events were also recorded on the Public
Seismic Network (PSN), a network of seismographs supported by the Australian Centre for
Geomechanics (ACG), which commenced in 2006 (Dent, Heal & Harris, 2006). Locations of the PSN
stations operating in 2022-24 are shown on the larger-scale maps following Figure 1 and listed in
Appendix 3. Data from these stations have been added to the GA data to derive new locations, usually
with a lower RMS of residuals, and therefore probably lower uncertainties in location. These re-
locations were made using the EQLOCL location program (© SRC, Melbourne) and the WA2 velocity
model (Dent, 1989), and were used to assign locations to the cluster groups.
While the uncertainty in these locations varies from earthquake to earthquake, it is considered that
in the majority of cases, relocations have uncertainties of < +/- 5 km.
The analysis here has been conducted in three sections: Events between 30-31°S (Zones A, B, C and L),
events between 31-32°S (Zones D, E and M) and events between 32-35°S (Zones F, G and H) - see
Figure 1.
3 Earthquakes between 30-31°S (Zones A, B, C, L)
3.1 Zone A, Cadoux region
Zone A (Figure 2) has been the site of intense seismic activity over the last 70 years, but was relatively
quiet in this study period. A damaging ML 6.2 earthquake occurred at Cadoux in 1979 (Lewis et al.,
1981), and an ML 5.5 event at Gabalong in 1955 (Everingham et al., 1982). A major group of events
also occurred near Burakin between 2000 and 2002 (Leonard, 2002).

AEES 2024 Conference, Nov 21-23 3
Three small events (MLs 2.2-2.4) in August and September 2022, occurred at location A2, the centre
of the major Burakin series of 2001-2002 (Dent et al., 2021).
An ML 4.4 event occurred 4 km south of
Cadoux in August 2022. The EQLOCL
relocation for this event is about 7 km SW
of the GA location and is shown in Figure 2
and listed in Appendix 2(a). It is close to 3
other smaller (ML~2.2) contemporaneous
events. This group is classified as an MSAS
group, rather than a cluster group
(Table 4).
3.2 Zone B, Beacon
During the 2-year study period, there
were two periods of high seismicity NW of
Beacon – in October/November 2023, and
in May/June 2024 (Figures 3a, b). The
group in May/June 2024 was the larger of
the two, with 25 events in May 2024, and these plot to the south of the 2023 group. It is suggested
that these events originated from location B2, and the earlier events from location B1, about 20 km
to the north.
Relocations of the two largest events (October 2023 and May 2024, both ML 3.3) moves each of them
about 5 km to the southwest, bringing them closer to cluster centres B1 and B2 (Figure 3b).
Relocations of some of the other events also bring them closer to these locations. A small event (ML
Figure 2. Seismicity in Zone A (Cadoux region)
Figure 3a. Seismicity in Zones B & C
Figure 3b. Seismicity northwest of Beacon

AEES 2024 Conference, Nov 21-23 4
2.2) which was located near cluster location B4 was a part of the November 2023 B1 sequence and is
probably poorly located.
3.3 Zone C, Koorda region
The plot of seismicity in zone C (Figure 3a) shows three cluster groups. Cluster C5, about 30 km SW of
Koorda, was first noted from relatively intense activity in April 2021, and activity has continued since
then, though it has declined. There were 12 events from this location in the study period, with the
majority, including the 2 largest events (both ML 2.7), occurring in the first 12 months.
The second cluster location is C1, about 20 km north of Koorda. This location exhibited intense cluster
activity in 2011-2012, but showed only occasional activity until April-May 2024, when 9 events
occurred (largest ML 3.3). C1 may represent the same location as two ML 4+ earthquakes which
occurred in 2004 and 2005.
The third cluster in zone C is SW of Bencubbin. This is a new cluster location, with 7 events in the
group, occurring between late November 2022 and January 2023, with the largest event (ML 2.9) at
the beginning of the activity. This group is identified as (new) cluster group C6 (Table 2)
3.4 Zone L, Mukinbudin – Bonnie Rock
A cluster of events occurred east of
Mukinbudin, mostly in November 2022, and is
identified as a new cluster location L7. There
were 24 located events, the largest ML 3.5. The
assigned location of L7 (Table 2) takes into
account the relocations of some of the larger
events in the group. It is notable that there have
been several other cluster sites active in the
Mukinbudin area over the last 5 years (L3, L5,
L6).
The group in the northwest of Figure 4, which
occurred mainly in October 2023, has also been
identified as a new cluster location L8. The
location of L8 has been based largely on
relocations of some of the larger events in this
group.
It is noted that the clusters east of Mukinbudin
(L7) and SW of Bencubbin (C6), about 60 km
apart, were active contemporaneously in
November 2022 (Table 5).
Figure 4. Seismicity in Zone L (Mukinbudin). Arrows link
original GA locations with their relocations.

AEES 2024 Conference, Nov 21-23 5
4 Earthquakes between 31°-32°S (Zones D, M & E)
Events in this region are shown on Figure 5a, with the Meckering, and “west of Quairading” regions
shown in more detail in Figure 5b.
4.1 Zone, D Bolgart – Westonia (31.0 – 31.5
oS)
The only event of ML 2.5+ was a solitary event north of Bolgart (Figure 5a). While the seismicity has
been low in the Bolgart region for the past 50 years or so, it contains the ML 5.1 Bolgart earthquake
of March 1952 (Everingham et al., 1982), and was a region of high seismicity between 1968 and 1971,
culminating in the Calingiri event (ML 5.7) of March 1970 (Gordon & Lewis, 1980).
A single ML 2.3 event near cluster location D8 on 1 August 2022 appears unremarkable, but this
location became the focus of a brief period of high seismicity (58 located events, largest ML 4.5) in
July & August 2024 (ie, immediately after the
period studied here). Relocations by the
author suggest the centre of the 2024 activity
is close to 117.61oE, 31.28oS, only about 1 km
from the GA location of the 2022 event.
Location D8 has been added to Table 1, which
shows previously identified clusters showing
activity in the 2022-2024 period.
4.2 Zone M, Meckering
The 11 events near Meckering are shown in
Figure 5b, and they can be considered as
continuing aftershocks of the damaging ML
6.8 event in 1968 (Gordon & Lewis, 1980).
They are on the hanging wall side of the
surface-rupturing reverse fault and seem to
define a north group (mostly in November
2022) and a southern group (mostly in June
2024), roughly correlating with the identified
cluster locations of M4 and M3.
Figure 5b. Seismicity Meckering to Balkuling
Figure 5a. Seismicity in Zones D, M & E

AEES 2024 Conference, Nov 21-23 6
4.3 Zone E
The only group of significance in Zone E is the group west of Quairading. This group, which crosses
westwards into Zone M, is shown in more detail in Figure 5b, and represents a continuation of activity
which began about 2 years earlier. This location was named E4 in Dent and Collins (2018), based on a
group of events in (2012). The plot of events in Figure 5b suggests a possible NW trend, as was also
noted for events in 2020-2021, when it was suggested (Dent, 2021) that the E4 location might be
better regarded as two locations, E4 (east) and E4 (west). An alternative possibility is that there may
be an elliptical or linear structure present. More precise earthquake locations (ie, locations using well-
sited arrays of close seismometers operating at high sampling rates) are required to resolve this.
More significantly, it is suggested that events at this location represent a renewal of activity which was
first noted as a significant swarm location in 1991 – 1992, when a cluster of 35 located events occurred
(largest ML 3.3, Dent & Collins, 2018). Other than one small event ENE of Kellerberrin (ML 2.3, July
2023), there do not seem to be any other events in Zone E.
Table 1. Cluster locations identified prior to 2023 and deemed active during this study
Place
Name
Location
Max
ML
Number
Date
Comment
Burakin
A2
117.05 -30.53
2.4
3
Aug-Sep 2022
Site active, 2001
N of Beacon
B1
117.75 -30.24
3.3
5
Oct-Nov 2023
Site active, 2009
NW of Beacon
B2
117.75 -30.40
3.3
38
May 2024
Site active, 2012
N of Koorda
C1
117.47 -30.64
3.3
10
May 2024
Site active, 2012
SW of Koorda
C5
117.25 -30.95
2.7
12
Spread over time
SE of Wyalkatchem
D8
117.63 -31.26
2.3
1
1 Aug 2022
Site active, 2024
W of Quairading
E4
117.25 -31.98
2.4
10
May 2023
Site active, 1992
SE of Newdegate
G3
119.16 -33.21
2.6
3
Oct 23-Jan24
Arthur River
G11
116.97 -33.37
4.1
158
Feb 2023
NW of Wagin
G12
117.14 -33.25
2.4
3
July 2022
Table 2. New cluster locations identified in this report (ie, since Dent & Collins (2023)
Place
Name
When
Max
Num
Location
SW of Bencubbin
C6
Nov 22 – Feb 23
2.9
7
117.77 -30.91
E of Mukinbudin
L7
Nov 22
3.5
24
118.41 -30.88
SE of Beacon
L8
Oct 23
3.0
7
118.08 -30.53
W of Brookton
F11
Aug 2022
2.4
4
116.92 -32.37
S of Narembeen
F12
Jan- Mar 2023
2.2
3
118.40 -32.18
SW of Corrigin
F13
Dec 2022
2.7
4
117.75 -32.46
SE of Corrigin
F14
Jan-Feb 2023
2.5
4
117.91 -32.39
N of Kulin
F15
Nov 2023
2.4
2
118.15 -32.62
SW of Lake Grace
G13
Jun-Aug 2023
2.6
7
118.24 -33.29
E of Gnowangerup
G14
Jun 2024
2.4
5
118.29 -33.95
SW of Gnowangerup
H4
Oct 2022
2.4
4
117.94 -34.04

AEES 2024 Conference, Nov 21-23 7
5 Earthquakes between 32°-35°S (Zones F,G and H)
5.1 Zone F, Brookton to Hyden (32°-33°S)
Seismicity in this zone was relatively minor and is shown in Figure 6. Five small cluster groups can be
seen, all of which are new.
A group of 4 small events (all in August 2022, largest ML 2.4) occurred W of Brookton (Figure 6). There
is no other recent seismicity near this location, and the approximate central point is here defined as a
new cluster location F11 (Table 2). Very few events occur west of this location, and these events may
represent the approximate western boundary of the “SWSZ”.
Two small events are seen S of Narembeen in early 2023 and a third occurred 2 days before the study
period began. All events were ML 2.2, and this location is here given the identity of F12 (Table 2).
Seven events, comprising two cluster groups, about 20 km apart, can be seen southwest, and south,
of Corrigin, mostly between December 2022 and February 2023. The largest event of the southwest
group was ML 2.7, and for the southeast group, ML 2.5. Relocations of these two events using
additional (PSN) data shows no significant errors present, and the events are assigned to two cluster
locations, F13 and F14 (Table 2) at the GA locations for the largest events respectively. Significantly,
these two clusters are basically contemporaneous, and listed in Table 5, with the seismicity within
each of them occurring between December 2022 and February 2023. However, any causal relationship
between the centres is not known.
There were two events north of Kulin (ML 2.2 and 2.4) in November 2023; this is also a new cluster
location, and is given the identity of F15 (Table 2).
5.2 Zone G, (33°-34°S, Katanning region)
Figure 6 shows an apparently isolated ML 2.7 event in April 2023, about 50 km east of Hyden. It is
listed in Table 4 as an isolated event, although it falls close to cluster location F6.
Two very significant groups of events occurred in Zone G (Figure 7a). The first, about 10 km SW of
Arthur River is continuing activity from an ML 4.8 event in January 2022, and the second, an ML 5.0
event east of Gnowangerup occurred in August 2023. The Arthur River event produced a clear InSAR
Figure 6. Seismicity in Zone F

AEES 2024 Conference, Nov 21-23 8
(Interferometric Synthetic Aperture Radar) signal (pers. comm., S. Valkaniotis, 2022, and reproduced
in Murdie et al., 2022), while only a vague signal resulted from the 2023 Gnowangerup event (pers.
comm., Dan Clark 2023). Note that an ML 4.8 event in October 2007, southwest of Broomehill, known
as the “Katanning” earthquake (Dawson et al., 2008) and shown in Figure 7a, also produced a good
InSAR signal and visible ground deformation.
5.2.1 The Arthur River seismicity
The activity during this period is a continuation of the seismicity following an ML 4.8 event on
26 January 2022 (Murdie et al., 2022). Events between July 2022 and June 2024 are shown in more
detail in Figure 7b. The largest events in this period were in February 2023 (ML 4.1), September 2023
(ML 3.6) and February 2024 (ML 3.6).
Up to 10 temporary seismographs were deployed in the area, and the seismicity for the first 9 months
of activity was discussed by Murdie et al., (2022) and Dent & Love (2022). Seismicity for the following
year was discussed by Dent & Collins (2023). As mentioned in Murdie et al. (2022), relocations of GA
solutions have often resulted in large shifts in location, some shifts approaching 10 km. Generally, the
new locations are west to SW of the GA locations. While trends within the local seismicity were hard
to determine, the seismicity broadly matched a tabular region identified by InSAR where an
approximately 2 cm ground uplift had occurred (Figure 7b), (pers. comm., S. Valkaniotis, 2022).
Two stations installed in the epicentral area shortly after the sequence commenced (AJ02, ARV4,
Figure 7b) have continued to operate into 2024. When their data are added to data from the GA
network, locations can be significantly improved. About 40 events since July 2022 have been relocated
in this manner, and relocations for the 12 events of ML 3.0 or greater (Table 3) are shown in Figure
7b. The largest event (ML 4.1) on 5 February 2023 relocates about 12 km westwards, to a location
close to G11, the approximate centre of seismicity identified in Dent & Collins (2022). The other ML 3-
plus events also relocate to within 2 km of this location. While good relocations of smaller events are
Figure 7a. Seismicity in Zone G

AEES 2024 Conference, Nov 21-23 9
distributed over the entire uplifted region, the majority of the seismicity seems to occur in the
southern portion.
Because there are insufficient data from close stations, the focal depths computed are unreliable.
However, the short S-P times at stations AJ02 and ARV4 indicate that the events are shallow, at about
3 km deep or less. Much of the seismic data collected in this region is still to be analysed, and refined
focal depths and epicentral trends may be published in the future.
As noted in Dent & Collins (2022), a cluster of 12 located events occurred in December 1989, about 15
km to the east of the 2022-2024 activity. The largest was ML 2.6, with a central point for the cluster
at 33.35oS, 117.21oE, about 11 km SW of Wagin (Figure 7a). This location is approximate because the
closest seismograph at the time was NWAO, about 80 km north of the epicentres.
Figure7b. Seismicity near Arthur River, with relocations of events greater than ML 3.0
Table 3. Arthur River events greater than ML 3.0, July 2022 – June 2024
Date/time
GA computed values
Relocation
LonoE
LatoS
ML
Dep.
RMS
LonoE
LatoS
Dep.
Pha.
2022-09-15_20:00:28.965
117.000
-33.337
3.0
2.1
0.68
116.984
-33.368
2.0
7
2022-12-25_17:47:56.144
117.032
-33.331
3.0
5.0
0.77
116.970
-33.363
3.3
7
2023-02-03_05:16:22.087
117.076
-33.376
3.2
5.3
0.83
116.972
-33.378
1.8
7
2023-02-05_00:39:57.733
117.084
-33.369
4.1
5.6
0.96
116.987
-33.372
1.9
8
2023-02-06_10:44:18.181
117.010
-33.352
3.0
5.0
0.78
116.971
-33.377
3.7
6
2023-09-01_06:07:36.36
116.989
-33.350
3.1
1.6
0.70
116.970
-33.360
3.4
8
2023-09-02_08:49:10.208
117.057
-33.340
3.6
5.0
0.93
116.995
-33.370
2.1
10
2023-11-10_05:09:19.747
116.978
-33.349
3.2
5.0
0.79
116.987
-33.362
3.7
5
2024-02-10_10:18:37.413
117.045
-33.360
3.0
5.0
0.84
116.989
-33.374
2.2
5
2024-02-10_10:20:11.956
117.061
-33.359
3.6
5.0
0.68
116.967
-33.369
3.3
5
2024-06-19_10:39:38.871
117.019
-33.361
3.1
1.7
0.95
116.989
-33.361
3.2
7
2024-06-21_20:31:58.128
117.011
-33.347
3.1
1.1
1.02
116.984
-33.365
3.3
9

AEES 2024 Conference, Nov 21-23 10
5.2.2 Gnowangerup area seismicity
The other group of important events in Zone G are those around an ML 5.0 event which occurred near
Mindarabin, about 30 km NE of Gnowangerup, on 5 August 2023. This region is shown in more detail
in Figure 7c. The earthquake caused major structural damage to the only farmhouse in the area. GA
did not locate any aftershocks of the event in the 5 months following the ML 5.0 event, although two
events in the previous month (both ML 2.6) could be foreshocks. However, the PSN station near
Dumbleyung (DBYG), ~70 km to the NW Figure 7a), detected 6 events in the following two days, with
the largest estimated at ~ML 2.3. These 6 events cannot be located with any reliability, because they
were not recorded by other stations - the GA station ONGER, (~15 km from the epicentre), was not
brought back into service until 22nd Aug., 17 days after the ML 5.0 event.
The PSN station at Gnowangerup (GNOT, Figure 7c) was reoccupied from 11 August 2023, 5 days after
the main event, and detected about 4 aftershocks in the first week of its operation. These all had S-P
times of close to 2.9 secs at GNOT. The largest of these, on 16 August at 18:26 hrs UTC, had an
estimated magnitude of ~ ML 2.2, and was also recorded on PSN stations at DBYG and PINW, and so
a location can be determined. This location (118.254oE, 33.837oS) is plotted on Figure 7c, and listed in
Appendix 1, and is within 1 km of the damaged farmhouse. It is probable that the main shock and
aftershocks all originated at close to this location. This location is within the stated margin of error for
the GA and Seismological Assoc. of Australia (SAA) locations of the main event, listed in Appendix 1.
There must have been many more small events as the farmer, whose house was damaged, reported
“almost non-stop” seismicity for about a week following the ML 5.0 event. A NNE orientated crack in
a gravel road, about 2 km south of the farmer’s house, was found by the farmer after the event. This
feature traversed the road and probably continued into bush areas either side of it (Figure 8).
This group of events is considered to be a Mainshock/Aftershock sequence and listed in Table 4. It is
not considered a cluster location. Occasional events well after the main shock (e.g. two events in May
2024, and another in July 2024) are probable aftershocks.
Figure 7c. Seismicity in the Gnowangerup area

AEES 2024 Conference, Nov 21-23 11
Significant clusters of small events (largest ML
2.3) have been noted near this location in the
past – ie, at the Wemyss Estate in 1991 and
Karingal in 2007 (Dent, 2008b).
A group of 5 events can be seen on Figure 7c,
approximately 40 km ESE of Gnowangerup.
They occurred between April and June 2024
and are assigned to a new cluster location G14
(Table 2).
5.2.3 Events southeast of Newdegate
Three events SE of Newdegate (ML 2.6, 2.5 &
2.3) may represent continuing activity from
cluster location G3 (Figure 7a). The largest
previous event at this cluster location was an
ML 4.3 event in June 2019, and there have
since been occasional events near there,
sometimes relatively large. This sequence,
which is classified as a “cluster”, has some
similarities with the 2023 Gnowangerup event
(classified MSAS), i.e., there was one large
event, while other events were infrequent and
spread out over many months.
Five events in June and August of 2023, about 30 km SW of Lake Grace, are allocated to a new location
called G13 (Table 2). The largest event was ML 2.6 and was the second of 3 events on 27 August 2023.
5.3 Zone H, (34°-35°S) Tambellup, Cranbrook – Rocky Gully
Seismicity in this region, south of 34°S, is shown in Figure 7c. It is a region of low seismicity, although
the Lake Muir events of 2018 were an exception to this. Only 3 cluster locations have been located in
this zone so far – H1 (N of Rocky Gully, Dent, 2014), H2 (NE of Tambellup, Dent, 2020), and H3 (SE of
Borden, Dent, 2021). In this study period, four small events SW of Gnowangerup occurred in October
2022 (Figure 7c). The largest was ML 2.4, and the average location is 34.04°S 117.95°E which is defined
here as a new cluster location H4 (Table 2).
6 Solitary events and Mainshock/Aftershock sequences
Events which may belong in this category are listed in Table 4. At times it can be hard to determine
into which category a group of events may belong. The most important factor is the difference in
magnitude between the “main” event, and the majority of the “coda” events. If the difference is 1
magnitude unit or greater, it will generally be classified as an MSAS sequence because “swarm”
sequences generally have several “main” events of similar size. In this report, the Arthur River
sequence is classified as a “swarm” as the two largest events were ML 4.8 and ML 4.1, and there were
a very high number of subsequent events. The 5 August 2023 ML 5.0 Gnowangerup event is classified
as an MSAS event. There were no located aftershocks at the time it occurred. However, approximately
Figure 8. Crack in north-south road east of Gnowangerup

AEES 2024 Conference, Nov 21-23 12
6 months beforehand, there was an ML 4.5 event close to the mainshock location.
The point to be taken is that, even if an event appears to be “solitary”, it may be related to a previous
event, which may have occurred months, years, or even decades beforehand.
7 Discussion
In the above analysis, events were determined to have originated from 10 cluster locations which
were previously recognised, and from 11 locations that have not been previously noted. The most
significant cluster groups (from Arthur River and NW of Beacon) belong to the former category –
although the seismicity recorded at Arthur River actually represents one continuing (but declining)
sequence. The most significant of the “new” cluster locations is probably that found east of
Mukinbudin (L7, Figure 4), which comprises about 24 located events, mainly in November 2022, the
largest ML 3.5.
It has been noted that contemporaneous seismicity is sometimes observed at neighbouring clusters.
While some connection could be envisaged for clusters within ~ 20km of each other, what could be
described as contemporaneous activity has been observed at separations of 60 – 70 km. An example
from the current study (Table 5) is the cluster pair E of Mukinbudin (L7) and SW of Bencubbin (C6),
where the separation is ~ 60 km. It is also seen between the NW of Beacon (B2) and north of Koorda
(C1) clusters, and between the Arthur River (G11) and NW of Wagin (G12) clusters. Similar
contemporaneous seismicity between the north of Hyden cluster (F1) and north of Holt Rock cluster
(F6) was noted by Dent (2021). A reason for contemporaneous seismicity is not clear. There do not
appear to be any geological structures which could potentially link the events. Perhaps the best
explanation is that continued shaking from one location has destabilised the equilibrium which may
exist in a neighbouring fault or fault complex.
Table 5. Suggested pairs/times of contemporaneous or related seismicity
Cluster
pair
Separation
(km)
Date
Region
Comment
F13, F14
20
Dec 2022 – Feb 2023
S of Corrigin
C1, B2
40
May 2024
N of Koorda & NW of Beacon
Also in 2012
F1, F6
40
Mar 2013
N of Hyden & E of Hyden
Ref. Dent (2018)
C6, L7
60
Nov – Dec 2022
SW of Bencubbin & E of Mukinbudin
G11, G12
15
Mar – Jul 2022
SW of Arthur R. & NW of Wagin
A2, A3
18
Sep 2000 & Sep 2001
NW of Cadoux
Leonard 2001
Table 4. “Isolated” and MSAS earthquakes July 2022 – June 2024 (ML >= 2.5)
Place
When
Max ML
Comment
Off Augusta
17/08/2022
3.3
Off southwest coast
Cadoux
21/08/2022
4.4
Has 3 small aftershocks?
Gnowangerup
05/08/2023
5.0
Suggested epicentre is 118.25 -33.84
SW of Southern Cross
08/11/2023
2.6
Similar to ML 2.8 event, November 2023
S of Goomalling
11/01/2023
2.6
N of Bolgart
04/01/2024
2.5
Near location of ML 5.1 event, March. 1952
NE of Holt Rock
18/03/2024
2.7
Near cluster location F6

AEES 2024 Conference, Nov 21-23 13
One interesting event was the “isolated” ML 2.5 event north of Bolgart, as it is close to the location of
an ML 5.1 event in 1950, and also relatively close to the Calingiri event of March 1970. As aftershocks
of large events can occur decades later, it is possible that this event is related to the 1950 Bolgart
event.
A possible related phenomenon is “rapid stress transfer”. This mechanism was suggested by Leonard
& Boldra (2001), to relate a sustained period of high seismicity from a location north of Cadoux (now
named location A3) in September 2000, with the onset of a sustained period of high seismicity west
of Burakin, beginning with an ML 5.2 event in Sept. 2001, (Leonard, 2002, Dent et al., 2021) at a
location now named location A2. A2 is ~ 20 km NW of A3, and this pair of clusters is also listed in
Table 5.
Relocations of events suggest that, in most cluster groups, all events could be placed at one central
location, considering the epicentral uncertainties. However, with some cluster groups, this is not the
case. For events in the Arthur River region, many of the events can be more accurately located because
of extra field stations deployed in the area, and the locations suggest an epicentral zone about 5 km
wide. There are suggestions of a NNE trend to epicentres within the zone, but more research is
needed. The fact that these events are contemporaneous suggests a single fault system causing the
seismicity. As it has not been possible to accurately locate events in most cluster groups, it is not
possible to identify epicentral trends within them, if they are indeed present. A recent well monitored
earthquake sequence from Jamestown, north of Adelaide (Love & Lade, 2024), provides an example
where this is possible. The largest event was ML 4.1, and the sequence defined an apparent NW
striking fault line about 1 km long, with events between zero and 1.2 km depth. Although the
geological setting is different, similar dimensions may apply to many of the SWA cluster groups noted
here.
There are other examples where cluster locations are closely spaced, and it is possible that they
represent end points of a single structure. An example is the cluster pair B1 and B2 NW of Beacon. B1
and B2 are separated by about 10 km, with a north-south trend. The most recent activity at B2 at the
southern margin of the cluster suggests it may be extending southwards. Another possible location
that is not a “point source” is E4, west of Quairading, where Dent (2021) suggested there may be an
E4 (east) and E4 (west), about 5 km apart. Better locations are needed to resolve this issue.
A potential problem arises when proposed cluster locations are close to the extent of uncertainties in
earthquake locations. This problem may be partly resolved if a sub-catalogue of relatively well-located
events arises from the SWAN (South West Australia Seismic Network) survey currently being
conducted by the Geological Survey of WA, in conjunction with the Australian National University
(Miller et al., 2023)
The observation that seismicity in the SWSZ generally occurs in well-defined clusters raises the
question as to whether there is a limit to the number of seismically active locations, or whether
anywhere in the region may host earthquakes in the future. While new cluster locations will likely be
identified in the coming years, given time it may become apparent that some areas never host clusters
and are essentially aseismic. At present it is not possible to say one way or the other, without a better
understanding of the underlying reasons why clustering of earthquakes is a feature of this part of
southwest Western Australia.

AEES 2024 Conference, Nov 21-23 14
8 Acknowledgements
We wish to express our gratitude for the assistance of the farmers and community of Gnowangerup.
Also, we appreciate the comments and editorial suggestions of Tamarah King.
9 References
Dawson, J., Cummins, P., Tregoning, P., and Leonard, M. (2008): Shallow intraplate earthquakes in
Western Australia observed by Interferometric Synthetic Aperture Radar, Journal of Geophysical
Research, 113, doi:10.1029/2008JB005807, 2008.
Denham, D., Alexander, L., Everingham, I., Gregson, P., R McCaffrey, & Enever J., (1987). The 1979
Cadoux earthquake and intraplate stress in Western Australia, Aust. J. Earth Sci., 34, 507-521.
Dent V.F., 1989. Computer generated crustal models for the southwest seismic zone, Western
Australia. Bur. Min. Res. Aust. Report 1989/43.
Dent, V., Heal, D. & Harris, P. (2006). A low cost seismograph network in WA. In Proc. Australian
Earthquake Engineering Society, Canberra.
Dent, V.F., (2008a) Graphical representation of some recent Australian Earthquake Swarms, and some
generalisations on swarm characteristics. In Proc. Australian Earthquake Engineering Society,
Ballarat.
Dent, V. F., (2008b). Improved hypocentral estimates for two recent seismic events in southwestern
Western Australia using temporary station data. In Proc. AEES 2008 Conference, Canberra, ACT.
Dent, V.F., (2012). Evidence for shallow focal depths and denser locations for three southwest seismic
zone earthquake clusters, 2011. In Proc. AEES 2012 Conference, Gold Coast, Qld
Dent, V.F., (2013). Using the “PSN” seismograph network in southwest Australia to improve
earthquake locations in the region. In Proc. AEES Conference 2013, Nov 15-17, Hobart,
Tasmania.
Dent, V.F., (2014) Earthquake clusters in southwest Australia in 2013-14. In Proc. AEES 2014
Conference, Lorne, Vic.
Dent, V.F., (2017) Earthquake clusters in southwest Australia seismic zone, June 2016 – May 2017. In
Proc. AEES 2017, Conference, Canberra.
Dent, V.F., (2018). An earthquake cluster east of Wyalkatchem, Western Australia, in late 2017. In
Proc. AEES 2017, Conference, Canberra.
Dent, V.F., (2021) Clustered Seismicity in Southwestern Western Australia, July 2020 -June 2021. In
Proc. AEES 2021 Virtual Conference, Nov 25 – 26.
Dent, V.F, & Collins, C.D.N., (2018). Clustered seismicity in southwest Australia, June 2012 – May 2013.
In Proc. AEES 2018 Conference, Perth, WA.

AEES 2024 Conference, Nov 21-23 15
Dent, V.F., Collins, C.D.N., & Murdie, R. (2021). Twenty years of earthquakes near Burakin in the
Western Australian Wheatbelt: A timeline of events in the Burakin seismic cluster of 2001 –
2002 and subsequent seismicity in the region. In Proc. AEES 2021, Virtual Conference.
Dent, V.F. & Collins, C., (2022). A review of seismicity in the southwest region of Western Australia,
July 2021–June 2022, with special reference to event clustering. In Proc. AEES Conference 2022,
Nov 24-25, Mt. Macedon, Vic.
Dent, V.F. & Collins, C., (2023). Continuing seismicity in the Arthur River area, Southwest Western
Australia (September 2022 - September 2023). In Proc. AEES Conference 2023, 23-25 Nov
Brisbane, Qld.
Dent, V.F., Heal, D. and Harris, P., (2006). A new network of low-cost recorders in WA. In Proc. AEES
Conference 2006, 24-26 Nov, Canberra, ACT.
Dent, V.F. & Love, D. N., (2022). A review of the seismicity near Arthur River, Southwest Western
Australia, January – July 2022. In Proc. AEES Conference 2022, Nov 24-25, Mt. Macedon, Vic.
Doyle, H. A. (1971). “Australian Seismicity”, Nature 234, 174–175.
Everingham, I. B., (1968) - Seismicity of Western Australia. Bur. Miner. Resour. Aust. Rep. 132.
Everingham, I. B., McEwin, A.J., & Denham, D., (1982). Atlas of Isoseismal maps of Australian
Earthquakes, Bureau of Mineral Resources Aust. Bulletin 214.
Gordon, F. R., and Lewis, J. D. (1980), “The Meckering and Calingiri earthquakes October 1968 and
March 1970”, West. Aust. Geol. Surv. Bull. 126, 229 pp.
Leonard M., & Boldra, P. (2001). Cadoux swarm of September 2000 – an indication of rapid stress
transfer? In Proc. AEES Conference 2001, Canberra ACT.
Leonard M., (2002). The Burakin WA earthquake sequence Sep 2000 – June 2002. In Proc. AEES
Conference 2002, Adelaide, SA.
Leonard M., (2008). One Hundred Years of Earthquake Recording in Australia. Bull. Seismol. Soc. Am.
98, 1458–1470.
Lewis, J. D., N. A. Daetwyler, J. A. Bunting, and J. S. Moncrieff (1981). The Cadoux earthquake, Western
Australia Geological Survey Report 1981/11, 133 pp.
Love, D.N.L., & Lade, B., (2024). The Jamestown earthquake M4.2 17th April 2024. In Proc. AEES
Conference 2024, Nov 21-23, Adelaide, S.A.
Miller, M. S., R. Pickle, R. Murdie, H. Yuan, T. I. Allen, K. Gessner, B. L. N. Kennett, and J. Whitney
(2023). Southwest Australia Seismic Network (SWAN): Recording Earthquakes in Australia’s
Most Active Seismic Zone, Seismol. Res. Lett. 94, 999–1011, doi: 10.1785/0220220323.
Murdie, R., Pickle, R., Yuan, H., Love, D., Dent, V., Miller, M., Whitney, J., (2022). Observations from
the 2022 Arthur River, Western Australia, Earthquake Swarm. In Proc. AEES Conference 2022,
Nov 24-25, Mt. Macedon, Vic.

AEES 2024 Conference, Nov 21-23 16
Appendix 1. Relocations presented in this report (excluding the Arthur River region)
Relocated
ML
Date / Time
(UTC)
Cluster
or Zone
GA
Comment
Lon
Lat
Lon
Lat
117.751
-30.394
2.2
2022-07-10_0330
B2
117.715
-30.404
NW of Beacon
117.769
-30.413
2.8
2022-07-25_2228
B2
117.736
-30.443
NW of Beacon
116.604
-32.462
2.4
2022-07-30_2141
Zone F
116.649
-32.405
N of Boddington
117.619
-31.284
2.3
2022-08-01_0046
D8
117.609
-31.277
SE of Wyalkatchem
118.675
-33.291
2.6
2022-08-04_2130
Zone G
118.592
-33.269
SE of Lake Grace
117.170
-30.849
2.2
2022-08-20_1115
Zone A
117.166
-30.857
Manmanning
117.066
-30.849
4.4
2022-08-21_0437
Zone A
117.122
-30.803
W of Manmanning3
116.926
-32.367
2.4
2022-08-26_1207
F11
116.936
-32.358
W of Brookton
117.044
-31.624
2.2
2022-09-12_1711
M4
117.040
-31.649
Meckering
117.958
-34.046
2.4
2022-10-24_0152
G14
117.951
-34.034
E of Gnowangerup
118.245
-33.274
2.3
2022-11-06_1302
G13
118.284
-33.240
Lake Grace
118.398
-30.873
2.8
2022-11-14_0335
L7
118.284
-33.240
Mukinbudin
116.995
-31.652
2.3
2022-11-16_2026
M4
116.999
-31.642
Meckering
118.406
-30.879
3.2
2022-11-17_2134
L7
118.444
-30.902
E of Mukinbudin
118.433
-30.875
3.5
2022-11-21_2347
L7
118.441
-30.824
E of Mukinbudin
117.764
-30.914
2.9
2022-11-29_0444
C6
117.778
-30.903
SE of Koorda
117.283
-32.038
2.2
2022-12-07_2046
Zone F
117.307
-32.048
ESE of Quairading
117.746
-32.461
2.7
2022-12-18_0414
F13
117.764
-32.438
SW of Corrigin
118.225
-33.837
4.5
2023-01-05_0512
Zone G
118.340
-33.783
East of Gnowangerup1,3
118.273
-33.825
4.5
2023-01-05_0512
Zone G
118.340
-33.783
East of Gnowangerup
117.961
-32.397
2.5
2023-02-05_2236
F14
117.917
-32.392
SE of Corrigin
117.002
-31.630
2.7
2023-02-21_0928
M4
117.018
-31.624
Meckering
118.224
-33.853
2.5
2023-02-27_1130
Zone
118.195
-33.853
E of Gnowangerup1
118.246
-33.844
2.5
2023-02-27_1130
Zone
118.195
-33.853
E of Gnowangerup
117.766
-30.423
2.7
2023-03-03_1441
B2
117.774
-30.439
NW of Beacon
117.759
-30.428
2.9
2023-03-03_1442
B2
117.753
-30.432
NW of Beacon
116.676
-32.078
2.1
2023-03-30_2200
Zone F
116.692
-32.058
west of Beverley
118.529
-33.928
2.4
2023-04-22_1238
G14
118.446
-33.915
east of Gnowangerup
117.008
-31.694
2.3
2023-05-05_0912
M3
117.017
-31.717
S of Meckering
117.218
-31.972
2.4
2023-05-15_0234
E4
117.188
-31.954
WNW of Quairading
118.172
-33.832
2.6
2023-07-27_2137
Zone G
118.174
-33.865
E of Gnowangerup
118.183
-33.861
5.0
2023-08-05_2134
Zone G
118.291
-33.804
E of Gnowangerup1
118.199
-33.861
5.0
2023-08-05_2134
Zone G
118.291
-33.804
E of Gnowangerup
118.254
-33.837
2.3
2023-08-16_0826
Zone G
—
—
E of Gnowangerup2
117.755
-30.259
3.3
2023-10-09_0845
B1
117.812
-30.215
NW of Beacon
117.742
-30.283
2.5
2023-10-09_1840
B1
117.750
-30.233
NW of Beacon
117.265
-31.971
2.0
2023-10-10_2000
E4
117.268
-31.987
W of Quairading
118.065
-30.522
3.0
2023-10-19_0150
L8
118.102
-30.517
SE of Beacon
117.763
-30.380
3.3
2024-05-19_0351
B2
117.793
-30.368
W of Beacon
117.75
-30.393
2.9
2024-05-19_0824
B2
117.767
-30.396
W of Beacon
118.234
-33.830
2.8
2024-05-20_0611
Zone G
118.204
-33.824
E of Gnowangerup
117.055
-31.708
2.5
2024-06-14_0147
M3
117.046
-31.688
Meckering
118.289
-33.947
2.4
2024-06-21_0000
H4
118.279
-33.944
S of Gnowangerup
1 Solution by Seismological Soc. of Aust. (SAA)
2 Not located by Geoscience Aust. (GA)
3 Solution in Appendix 2

AEES 2024 Conference, Nov 21-23 17
Appendix 2(a) EQLOCL solution for the Cadoux event, 21 August 2022
Date 2022-08-21 Origin Time 0437 1.93 +- 0.88 Zone 50
Easting 506.29 +- 5.77 Longitude 117.066
Northing 6587.14 +- 12.16 Latitude -30.849
Depth 7.09 +- 21.27
Arrival times = 9 S.D. = 0.144 Seismographs = 6
Nearest recorder = 41.9 km Gap = 135.9 deg Accuracy = B
Earth Model WA2 Run by: VFD
168 km NE ( 44 deg) of PERTH 3 km W (272 deg) of Manmanning Assign ML 4.4
DATA USED
Code Wave AT +- WT CT DT Dist Azim Ad Ae
KORD P 8.72 0.10 1.35 8.86 -0.15 41.9 94 9.7 9.7
KORD S 13.74 1.00 0.77 13.67 0.07 41.9 94 9.7 9.7
BLDU P 9.00 0.10 1.35 9.06 -0.06 43.1 307 9.8 9.8
BLDU S 14.20 1.00 0.77 14.00 0.20 43.1 307 9.8 9.8
KLBR P 19.00 0.20 1.09 19.14 -0.14 105.3 141 4.0 4.0
KLBR S 31.40 1.00 0.71 31.07 0.33 105.3 141 4.0 4.0
WATG P 19.90 0.10 1.25 19.77 0.13 109.1 83 3.8 3.8
AKUL P 35.20 0.20 1.02 35.22 -0.02 226.6 153 -42.2 42.2
NWAO P 35.75 0.20 1.02 35.73 0.02 230.8 176 -42.2 42.2
Deferred Data
WATG S 33.60 1.00 0.71 32.14 1.46 109.1 83 3.8 3.8
AKUL S 63.80 1.00 0.67 60.10 3.70 226.6 153 -40.3 40.3
NWAO S 64.80 1.00 0.66 60.98 3.82 230.8 176 -40.3 40.3
ONGR P 51.70 0.30 0.90 50.97 0.73 356.9 159 -42.2 42.2
Appendix 2(b) SAA solution for the Gnowangerup event, 05 August 2023
EQ Date: 2023-08-05 2134 43.20 ± 0.27 Gnowangerup 18km NE Mag: MLv 5.4
Longitude: 118.1830 ± 1.65 km
Latitude: -33.8608 ± 1.10 km Depth: 5.00 ± 1.75 km(Const.)
Arrivals: 16/22 StdDev: 0.404 Sites: 9/11
Nearest: 64.0 km (DBYG) Gap: 138.9° Quality: P Accuracy: C
Run by: DL Run Date: 2023-08-08 eqFocus 4.5.1 Earth Model: WA2
Active Arrivals:
site phase time wt calc residual dist travTime res/tt
DBYG P 2134 53.75 ± 0.0 2.7 53.68 0.07 64.03 10.55 0.634
DBYG S 2135 02.06 ± 0.0 2.7 61.35 0.71 64.03 18.86 3.760
ARV5 P 2135 03.22 ± 0.0 2.6 63.78 -0.56 127.33 20.02 -2.797
ARV5 S 2135 18.64 ± 0.0 2.6 79.13 -0.48 127.33 35.45 -1.359
AUALB P 2135 03.99 ± 0.0 2.6 63.98 0.01 128.89 20.79 0.071
AUALB S 2135 19.62 ± 0.0 2.6 79.48 0.14 128.89 36.42 0.393
AUKUL P 2135 04.50 ± 0.0 2.6 64.45 0.05 132.13 21.30 0.235
AUKUL S 2135 19.57 ± 0.0 2.6 80.31 -0.74 132.13 36.37 -2.037
NWAO P 2135 04.90 ± 0.0 2.6 65.01 -0.11 136.17 21.70 -0.502
NWAO S 2135 21.32 ± 0.0 2.6 81.30 0.03 136.17 38.13 0.086
RKGY P 2135 05.44 ± 0.0 2.6 65.31 0.13 138.46 22.24 0.599
RKGY S 2135 21.71 ± 0.0 2.6 81.82 -0.11 138.46 38.51 -0.295
KLBR P 2135 21.33 ± 0.0 2.5 80.53 0.81 254.84 38.14 2.117
KLBR S 2135 48.92 ± 0.0 2.5 108.67 0.25 254.84 65.72 0.385
KMBL P 2135 43.64 ± 0.0 2.4 103.84 -0.19 443.82 60.45 -0.313
AUKAL P 2135 46.17 ± 0.0 2.4 106.18 -0.01 462.85 62.97 -0.023
Deferred Arrivals:
site phase time wt calc residual dist travTime res/tt
PINW P 2135 13.16 ± 0.0 2.5 72.01 1.15 186.75 29.96 3.823
PINW S 2135 35.54 ± 0.0 2.5 93.64 1.91 186.75 52.35 3.640
COR2 P 2135 14.86 ± 0.0 2.5 73.88 0.99 200.91 31.67 3.122
COR2 S 2135 38.02 ± 0.0 2.5 96.97 1.05 200.91 54.82 1.922
KMBL S 2136 28.39 ± 0.0 2.4 149.67 -1.28 443.82 105.19 -1.215
AUKAL S 2136 31.19 ± 0.0 2.4 153.80 -2.61 462.85 107.99 -2.414

AEES 2024 Conference, Nov 21-23 18
Appendix 3. Public Seismic Network stations in operation during 2022 - 2024
Code
Latitude
Longitude
Opened
Location, remarks
AJ01
-33.3582
116.9756
2022-02-19
Arthur Rv. -Rifle Range – intermittent only
AJ02
-33.3470
117.0028
2022-02-20
Arthur Rv. -Pascoe’s - closed 06 Aug. 2024
AJ03
-33.3769
116.9929
2022-02-21
Arthur Rv. -Burgess’ – closed 19 July 2022
ARV4
-33.3788
116.9628
2022-03-10
Arthur Rv. -Bird’s
ARV5
-33.3528
116.9526
2022-06-08
Arthur Rv. -Rocky Ridge closed 19 July 2022
CADX
-30.7692
117.1360
2014-02-11
Cadoux
COR2
-32.0857
117.7457
2017-08-05
Corrigin – Caporn’s
DBYG
-33.4231
117.7333
2021-07-27
Dumbleyung
GNOT
-33.9384
118.0071
2017-04-27
Gnowangerup Town (reopened 2023-08-11)
MEKS
-31.7018
117.0384
2018-12-11
Meckering South
MECK
-31.6316
117.0074
2015-12-03
Meckering
PINW
-32.4798
117.0010
2019-11-13
Pingelly Woolshed (replaces PING)
STHX
-31.2305
119.3263
2021-06-16
Southern Cross
TMBL
-34.0430
117.6380
2017-04-27
Tambellup – closed Feb. 2023