I've had to think hard on how to put this together. I really want to share what I do with everyone, but experiences in the past (when I did my fiction writing a decade or so back) make me incredibly hesitant to reveal too much information. Hopefully I can find a balance here; please let me know if there isn't enough information in this in order for you, the reader, to actually understand what I am talking about!
Searching the Archives
In my previous blog post I left off having decided to start looking at historical earthquakes in New Zealand for a prospective, albeit never begun, Masters project at Plymouth University. About a month later (early April 2018) I began to search the internet to see what I could find. The first, and most obvious port of call, was the GeoNet website. On the website you can find all sorts of information about earthquakes: live seismograms, recent earthquakes, slow slip events and much more. The two pages of most use to me however are the historical events, which shows a variety of significant earthquakes which have struck New Zealand between 1848-present, and the earthquake search which enables you to search for earthquakes within the GeoNet database. I'll get back to database later in this blog post.
Both of these pages are very powerful. The historical events summarises all sorts of quakes, from significant 19th century quakes (1848 Marlborough, 1855 Wairarapa, 1868 Cape Farewell & 1888 North Canterbury) to more moderate 20th century events (1966 Seddon, 1976 Waikato & 1990 Lake Tennyson). New Zealand's more recent seismicity has a far greater share of the list's contents, because a) recent seismicity has been the most active to strike New Zealand in 80-90 years and b) most people are going to interested in reading about the more recent significant earthquakes than those in distant living memory or beyond living memory.
 |
| Isoseismal Map of the 1868 Cape Farewell Earthquake (Downes & Dowrick, 1995) |
And herein lies the problem for New Zealand's historical catalogues. There are three main sources available for historical quakes in Aotaeroa: the GeoNet earthquake database (also known as the National Earthquake Information Database, or NEID for short); the two editions of Gaye Downes & David Dowrick's Atlas of Isoseimal Maps of New Zealand Earthquakes (published 1995 & 2014); & George Eiby's An Annotated List of New Zealand Earthquakes (published 1968). The latter author also has a couple of papers documenting earthquakes which occurred in the early years of New Zealand's historical after the Pākehā arrived in the early 20th century, whilst there are a myriad of papers documenting individual historical earthquakes from different disciplinary perspectives (seismology, tectonics, ground motion, engineering geology, etc.)
This is a fantastic start and in fact the available sources mean that historical earthquakes post-WW2 are fairly well documented, with all earthquakes above magnitude 6.0 known, and many more moderate (magnitude 4.5-6.0) earthquakes also documented. Many of these events are not included in GeoNet's historical events page (e.g. 1948 Mw 6.4 Waiau, 1962 Mw 5.9 Westport, 1974 ML 4.9 Dunedin & 1993 Mw 6.2 Ormond), but can be found in the NEID.
Isoseismal Map of the 1974 Dunedin Earthquake (Downes & Dowrick, 2014)
However, for the region targeted for the prospective Masters project back in 2018, there had been no significant quakes since a Mw 5.9 in 1951 damaged a township familiar with seismicity in the 20th century. This meant that, with a fairly complete catalogue after 1951, to find other earthquakes which may have adjusted the stress in the region I had to look earlier. This meant investigating earthquakes which may not be in the small collection of databases and catalogues available.
Another important discovery from the above sources was found in Downes & Dowrick (2014). In the preface to the Second Edition, the final paragraph notes that "there are many deep and some shallow earthquake with magnitude M≥6 for which there are insufficient data for an isoseismal map", as well as "large earthquakes in remote locations... or locations that were sparsely populated may not have bene recognised yet, as in-depth research on parts of the historical record, principally, 1855-1900, is incomplete." Both the need to look for specific regional quakes prior to 1951, and this paragraph, was encouragement to see just what could be found. Now it was just to find sources of information to do this.
By luck I happened upon a website which may be able to help and I have continued to use ever since. This is Papers Past, a New Zealand government website containing thousands of different digitised newspapers, magazines, journals, letters, diaries and parliamentary papers from the 19th, 20th & early 21st centuries. A treasure trove for researchers into New Zealand's post-colonisation history, it also contains plenty of references to earthquakes. One journal in particular, the Transactions and Proceeding of the Royal Society of New Zealand, contains in every edition from 1869-1902 tables of earthquakes in the respective year felt in the towns & settlements of New Zealand. These are an invaluable source for any wannabe researcher into New Zealand's historical seismicity, and they were one of the first gold mines I happened across - in fact it is the basis of much of my 19th century research.
However my main focus initially was on using the newspapers found in the online archive. Within a week of commencing my research I had got a brief overview of seismicity from the 1900s decade (1901-1910) using issues of the New Zealand Herald newspaper, based in Auckland. Further searching revealed that many quakes were missing, and with my foci changing over the weeks and months that decade still requires a lot of work.
Page 5 of the Monday, September 3 1888 issue of The Press newspaper (Christchurch), showing the some of the articles on the North Canterbury Earthquake two days prior (The Press, 1888)
For the first year and a half I did not have a specific aim besides trying to find as many earthquakes as possible. Due to my increasing understanding of existing knowledge of New Zealand's historical seismicity, I set an arbitrary end date of 1929 (March 1929 Arthur's Pass & June 1929 Buller Earthquakes were the two most significant earthquakes to strike New Zealand in at least a quarter of a century, and in the case of the latter since 1855). A beginning date for the catalogue I was gradually constructing was post-1855 (the Mw 8.1-8.2 Wairarapa Earthquake is the largest quake in post-colonisation New Zealand's history), and currently it is 1862 (the year of earliest quake I have in my catalogue).
By the end of last year I had decided that I must recommence on my education after a year of retail work & gradual recovery from my final year at Plymouth. I began to make enquiries, both in the UK and abroad, with a vague idea of wanting to do a Masters project on historical New Zealand seismicity. At about this time I decided to take a look into seismicity in the latter part of my catalogue's temporal range. In the process of searching I came across a few earthquakes which caught my attention. An email sent to New Zealand scientists in January of this year proved the spark to deciding on two possible Masters projects. Further enquiries ruled out one option - it would require personally looking through archives in New Zealand to find further sources of information on the earthquake, despite the apparent importance of this quake to seismic hazard in New Zealand - and added a lot of possibilities towards the other option.
At present it is still early days in putting together the Master project; for a start it is yet to be proposed, owing to the course not yet commencing. Data collection is still ongoing, although it is making good and steady progress. What feels most exciting to me is being able to share a portion of what I have found*, and perhaps hint at just how much more is yet to revealed.
At present my All Quakes Database (which ironically excludes those already documented in Downes & Dowrick or the NEID) contains ~1550 individual earthquakes between 1862-1929. Recent data acquisitions (via GNS Science and a personal book acquisition) reveal that in reality, there most likely is a sum four or five times greater than that total to be found and documented. Many of these will most likely only have one felt location with no relevant information from which to derive an estimated intensity, but a sizeable minority will prove helpful in at bare minimum producing isoseismal maps, and at best relatively reliable estimates of location, magnitude and depth.
My desire to complete a Masters project on a small aspect of this research is twofold: to prove to myself that I can produce something worthy of being put out there into the wide scientific world, and to prove to others that what I am attempting to do is worthwhile. A catalogue of moderate and significant earthquakes is all very well and good, but it needs to be applied to things which have relevance to people today. And this is the task I have decided I wish to take on.
Final Note
I shall endeavour to share these holiday finds with you all soon. One of these was indeed an extraordinary find, owing both to it's contents and most certainly it's age. Another was written by the most popular writer on seismicity at the time of it's publication, and contains some beautiful plates. The third is a more recent publication (albeit nearly three decades older than myself) on a really significant New Zealand earthquake and was a nice find to accompany the others.
*This is a fun example of choosing the correct word. Technically speaking I am finding these quakes, but only because they have been forgotten or neglected in terms of research. A term I often unintentionally use is discover which would infer I was the first person to feel the quake, which would be impressive given I would need to be at least 70 years older than I am. Perhaps find and rediscover are the best terms to use, as I am both finding references to them, and in doing so rediscovering earthquakes felt by New Zealanders 90 or more years ago.
Literature References
Downes, G.L., Dowrick, D.J. 1995. Atlas of Isoseismal Maps of New Zealand Earthquakes. Institute of Geological & Nuclear Sciences monograph 11. Lower Hutt: Institute of Geological & Nuclear Sciences.
Downes, G.L., Dowrick, D.J. 2014. Atlas of Isoseismal Maps of New Zealand Earthquakes - 1843-2003. Second edition (revised). Institute of Geological & Nuclear Sciences monograph 25. Lower Hutt: Institute of Geological & Nuclear Sciences.
Eiby, G.A. 1968. An Annotated List of New Zealand Earthquakes, 1460-1965. New Zealand Journal of Geology and Geophysics. 11:3, p. 630-647.
Eiby, G.A. 1968b. A Descriptive Catalogue of New Zealand Earthquakes, Part 1 - Shocks Felt before the end of 1845. New Zealand Journal of Geology and Geophysics. 11:1, p. 16-40.
Eiby, G.A. 1973. A Descriptive Catalogue of New Zealand Earthquakes, Part 2 - Shocks Felt from 1846 to 1854. New Zealand Journal of Geology and Geophysics. 16:4, p. 857-907.
Picture References
Downes, G.L., Dowrick, D.J. 1995. Atlas of Isoseismal Maps of New Zealand Earthquakes. Institute of Geological & Nuclear Sciences monograph 11. p. 29. Lower Hutt: Institute of Geological & Nuclear Sciences.
Downes, G.L., Dowrick, D.J. 2014. Atlas of Isoseismal Maps of New Zealand Earthquakes - 1843-2003. Second edition (revised). Institute of Geological & Nuclear Sciences monograph 25. p. 604. Lower Hutt: Institute of Geological & Nuclear Sciences.
The Press (Christchurch, New Zealand), 1888. "Earthquake", 3 September 1888, p. 5. Accessed via: https://paperspast.natlib.govt.nz/newspapers/press/1888/09/03/5, National Library of New Zealand.
No comments:
Post a Comment