1985 north Tanami earthquake hunt
Tamarah King
Hi all,
I’ve been revisiting deep earthquakes in the GA catalogue, and I’ve noticed a Mb 5.2 earthquake in the northern Tanami in 1985 with a 33km depth (https://earthquakes.ga.gov.au/event/ga1985rvmtru).
I’ve looked through literature but can’t find any mention of this earthquake. I checked the annual BMR reports (https://aees.org.au/annual-seismological-reports/) and it seems to be missing from the 1985 report. I checked the maps and tables from the 1984, 1986 and 1987 reports and it’s also not there.
Does anybody know anything about how this earthquake ended up in the catalogue but seems absent from the literature? I’d guess the GA record is incorrect? If anybody does remember this event, I’m looking for some sense of how reliable the 33km depth is, whether that event was confidently in the 30km range rather than the 0-10 km range.
Also just a note, I often find those annual BMR/GA/Mundaring seismicity reports incredibly useful. Huge thanks to anybody who spent time putting them together over the years.
Many thanks,
Tamarah
Paul Somerville
| 1.99E+11 | ISC | 1985 | 9 | 10 | 11 | 57 | 3 | 130.24 | -18.05 | 33 | 5.07 | MW | 5.2 | mb | 5.2 | 5.07 | nan | nan | nan |
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Tamarah King
Hi Paul,
Thanks for that, I hadn’t thought to cross-check with the agency listed in the NSHA18 (the event is in both GA online and NSHA18 catalogues).
I’ve just searched the ISC catalogue (http://www.isc.ac.uk/iscbulletin/search/catalogue/interactive/) and it seems the only event coincident with that location (see map below) occurred in 2010 (http://www.isc.ac.uk/cgi-bin/web-db-v4?event_id=17311501&out_format=IMS1.0&request=COMPREHENSIVE). There’s no 2010 event in the GA or USGS catalogues for that location, and the 2010 ISC event has no magnitude but does have a depth of 22.7 km. There’s no 10/9/1985 events in the ISC catalogue for northern Australia that I can find.
I don’t really need to go too far down this rabbit hole, I imagine it’s a simple mistake somewhere along the line between ISC and GA. Rather odd though!
Tamarah
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cdncollins
Tamarah King
Hi Dmitry and Col,
Thanks for the detailed detective work Dmitry! Also thanks to Kevin and Gary who got in touch with similar hypotheses about the errant New Britain earthquake popping up in the Tanami. As a non-seismologist I’ve thoroughly enjoyed watching this earthquake hunt play out, and learning how/why it was anomalous. It’s useful to know I can have a healthy amount of scepticism if I find any other earthquakes that don’t correlate across different catalogues.
All the best and thanks again,
Tamarah
From: Dmitry Storchak <dmi...@isc.ac.uk>
Sent: Wednesday, 14 July 2021 6:51 PM
To: Col Lynam <col....@gmail.com>
Cc: Tamarah King <tamara...@gmail.com>; Adrienne Moseley <Adrienne...@ga.gov.au>; aee...@googlegroups.com; Gary Gibson <ga...@earthquake.net.au>
Subject: Re: Fwd: [aees] 1985 north Tanami earthquake hunt
Dear Colin and colleagues,
Thank you for your enquiry regarding the missing M5.2 "earthquake" in Australia. I know that you guys cherish each single one that happens in your country. Here you are up for a disappointment, I am afraid. Please see the extract from the old ISC Bulletin below :-)
OLD ISC (SHOWN HERE FOR HISTORICAL PURPOSES ONLY)
Event 515477 Northern Territory
Date Time Err RMS Latitude Longitude Smaj Smin Az Depth Err Ndef Nsta Gap mdist Mdist Qual Author OrigID
1985/09/10 11:57:03.90 -18.0500 130.2400 33.0f 16 130 15.00 164.00 m i uk ISC 1136662
Magnitude Err Nsta Author OrigID
mb 5.2 1 ISC 1136662
Sta Dist EvAz Phase Time TRes Azim AzRes Slow SRes Def SNR Amp Per Qual Magnitude ArrID
NAU 14.53 250.0 P 12:00:33.0 3.8 T__ _e 15844281
NAU 14.53 S 12:06:55.0 ___ _e 15844282
YOU 22.88 138.0 P 12:02:04.0 -1.7 T__ __ 15844283
CAN 23.94 140.0 P 12:02:16.9 0.9 T__ __ 15844284
MAT 54.81 8.0 P 12:06:40.0 6.9 T__ __ 15844285
(0)
MAT 54.81 8.0 P 12:06:40.0 6.9 T__ 37.2 1.40 _e mb 5.2 15844286
GBA 60.84 298.0 P 12:08:02.0 46.2 T__ __ 15844287
VAR 63.00 312.0 P 12:07:20.9 -9.2 T__ __ 15844288
BNG 111.98 268.0 PKP 12:14:26.7 -69.8 ___ 45.0 1.00 ci 15844289
BNG 111.98 12:15:34.5 ___ _i 15844290
BNG 111.98 pPKP 12:15:44.5 -3.4 ___ _i 15844291
WTS 124.48 321.0 PKP 12:15:06.0 -53.8 ___ _e 15844292
WTS 124.48 sPKP 12:16:19.0 5.2 ___ _e 15844293
ETA 131.61 326.0 PKP 12:15:25.4 -48.1 ___ _e 15844294
ETA 131.61 326.0 PKP 12:15:25.4 -48.1 ___ _e 15844295
ECP 131.94 325.0 PKP 12:15:27.5 -46.6 ___ 148.0 1.10 _e 15844296
ECP 131.94 325.0 PKP 12:15:27.5 -46.6 ___ 148.0 1.10 _e 15844297
ECB 132.07 326.0 PKP 12:15:27.1 -47.2 ___ 69.0 1.20 _e 15844298
ECB 132.07 326.0 PKP 12:15:27.1 -47.2 ___ 69.0 1.20 _e 15844299
SJG 164.41 87.0 PKP 12:16:08.0 -56.6 ___ _e 15844300
Sadly, this "earthquake" was inadvertently "invented" by my predecessors at the ISC. There was/is a routine operational process called "search" at the ISC where our analysts are trying to make use of all remaining station readings (reported to us) that haven't been associated to any already reported earthquakes. Sadly, on this occasion the ISC analysts of 1987 vintage did not recognise that many of the station readings of this "event" were in fact readings of secondary seismic waves from the preceding real moderate earthquake in New Britain Region that in 1987 was known to be recorded by 238 stations. Today it looks like this:
Event 515476 New Britain region
Date Time Err RMS Latitude Longitude Smaj Smin Az Depth Err Ndef Nsta Gap mdist Mdist Qual Author OrigID
1985/09/10 11:52:53.30 -6.3900 149.8100 3.0 uk MOS 1136657
1985/09/10 11:52:58.10 -6.5000 149.9000 uk PEK 1136659
1985/09/10 11:52:58.40 -6.4160 149.9600 41.0 152 uk NEIC 1136660
1985/09/10 11:53:00.70 1.150 -6.4150 150.0080 5.9 4.5 55 47.0 6.0 221 206 ke EHB 11272949
1985/09/10 11:52:58.74 0.46 1.911 -6.3243 149.9414 5.225 4.994 59 33.1 2.06 294 274 18 1.50 161.16 m i ke ISC 1136661
(#PRIME)
(#PARAM pP_DEPTH=33+5)
Magnitude Err Nsta Author OrigID
Mb 5.5 10 MOS 1136657
Ms 5.0 4 MOS 1136657
MS 5.1 PEK 1136659
mb 5.5 NEIC 1136660
MS 5.1 NEIC 1136660
mb 5.4 0.1 38 ISC 1136661
MS 5.0 0.1 10 ISC 1136661
The change in the ISC Bulletin has come as part of the Rebuild mega-project that we ran at the ISC for 10 years and completed in 2020. The phantom M5.2 "event" of interest has been banished whilst the majority of its "station readings" re-associated with the real event in New Britain that now has 274 associated station readings instead of 238 in the past. For example, station readings of
YOU, CAN fit there as PcP;
MAT as ScP;
GBA as P;
BNG, WTS, ECP, ECB and SJB as various branches of PKP/PKS.
This explains why you can no longer find the 1985/09/10 M5.2 event in the rebuilt ISC Bulletin. If GA still has a record of this earthquake with reference to the ISC, than we apologise for being a cause and kindly ask GA to remove it.
I did not mean to criticise my colleagues-predecessors at the ISC. Back in 1987 they had very little chance of catching this "event" automatically. Sadly, this event passed their manual review on some sunny Friday afternoon. At the ISC, we now have a dedicated process that aims to identify and catch similar instances before their publication.
Best wishes to all,
Dmitry
Dr. Dmitry A. Storchak
Director
International Seismological Centre (ISC)
United Kingdom
www.isc.ac.uk
+44 (0)1635 861022
The ISC is a Charitable Incorporated Organisation (CIO)
registered with The Charity Commission for England & Wales,
registered charity number: 1188971.
On 10/07/2021 23:56, Col Lynam wrote:
Hi Dmitry, nice puzzle about a missing Aust event in the ISC CATALOG. Have you got access to the reason why the M5.2 W. AUST has been deleted?
Cheers Col lynam
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