Earthquake Weather

Wellington’s recent run of hot, humid and light-wind days has brought talk of “earthquake weather” back into conversations recently. The subject even popped up on Kim Hill’s Saturday morning show on National Radio yesterday.

Hill was firing on all cylinders for most of her programme and her sometimes irritating interruption of her subjects was working very successfully in producing a conversational type of show. She wandered through a multitude of subjects such as coffee importing, books, gifts, food and sport in a thoroughly entertaining fashion. The conversation with food expert Ruth Pretty was highly informative, with Hill surprising Pretty with a few potato tips of her own. The discussion about Moby Dick was another conversational highlight of the show. Only during the sport discussion with Ken Laban did she end up “out of synch” with her guest, causing Laban’s organised presentation to sometimes falter with her interruptions.

Kim Hill raised the topic of earthquake weather through an anecdote of her time on the West Coast, in which discussion of its existence was attended by the timely occurrence of a shake.

To a certain extent, the concept of earthquake weather can be self-fulfilling, with people noticing and reporting more earthquakes on quieter wind-free days. In addition, the restless nights during humid weather cause fewer people to sleep through earthquakes that occur during the night hours. But there could be more to it than that.

At first, it might seem odd that the weather might be associated with the release of tectonic pressure in an earthquake. In fact, many seismologists of the closed mind variety instantly dismiss the possibility.

However, there have been members of that fraternity who have considered and studied the possibility. So far, nothing has been proven conclusively, but some interesting aspects of the meteorological relationship have been indicated.

One of New Zealand’s scholarly scientists of last century, the late George Eiby briefly mentioned the subject of earthquake weather in his book “Earthquakes”. This is not surprising, as George had a lively mind and anyone who heard his highly entertaining after-dinner speeches at various events such as the annual dinner of the The Royal Astronomical Society of New Zealand would know that his scientific mind was not closed.

Eiby mentioned that a Japanese study of 18 major earthquakes over a 530 year period found that 12 of the events occurred on fine days, 2 on cloudy days and 4 on rainy days. He added that this inconclusive study told us more about the Japanese climate than it did about earthquakes.

Charles Richter, remembered by his Richter Scale for measuring earthquake intensity noted that minor shocks increase at the beginning of California’s rainy season, when large air masses are constantly changing air pressure values. However, Eiby pointed out that there didn’t seem to be a corresponding pattern of triggering undersea earthquakes during the daily tide changes, which cause a ten times greater change in pressure on the sea bed than the air pressure changes cause on the land.

An indirect relationship between weather and earthquakes was suggested when heavy rain in the Bay of Plenty deposited up to a billion tons of floodwater in the area in 2004. A swarm of earthquakes near Lake Rotoiti between July 18th and August 8th caused additional damage to houses and roads, and triggered numerous landslides. Dr Martyn Reyners of IGNS suggested that the sheer weight of the water could have triggered earthquake activity in the earth’s thin crust in the area.

In the case of the three Matata earthquake swarms and flood earlier this year, the earthquake activity had commenced before the flash flood occurred. So, while the shaking may have contributed to the residents’ woes, there was no causal relationship between the two.

So, while some tantalising relationships between weather and earthquakes may exist, it seems that there is no definitive “earthquake weather.” Nevertheless the concept persists, and it was widely remarked upon in the East Coast area during the 1960s and 1970s, mainly by older people who recalled the 1931 Napier earthquake which occurred during a lengthy period of warm summery weather. The clement weather greatly assisted the recovery and cleanup activity throughout the Hawkes Bay and Gisborne regions, and possibly reinforced the view that earthquake weather is hot, still and humid conditions.

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