Edgecumbe New Zealand 1987 (CAR)
On the afternoon of Monday, March 2, 1987, at 1:42 pm local time, an earthquake of moment magnitude (Mw) 6.5 and focal depth of 8 to 15 km (depending on reporting seismological agency), struck the Bay of Plenty region of New Zealand (northern part of New Zealand’s North Island).
The earthquake was associated to a normal faulting mechanism in active extension in the Taupo volcanic zone, a back arc basin generated by the Hikurangi subduction zone beneath the North Island.
In the Rangitaiki Plains the rupture reached the ground level creating a 7km surface rift that was over one meter wide (Edgecumbe fault); the ground level in proximity of the epicenter dropped up to 2 meters during and immediately after the earthquake.
The epicenter (38.02°S, 176.92°E) was located between the towns of Matata (north-west) and Edgecumbe (south-east).
Numerous foreshocks preceded the main shock, the strongest (ML 4.9) occurred 7 minutes earlier (at 1:35 pm), and probably saved the lives of many people. The main shock was followed in the same day by four aftershocks with magnitude greater than 5.
Ground shaking in the epicentral region was more vigorous than would have been expected for an event of such magnitude probably due to its shallow focus.The strongest effects were felt in the Rangitaiki Plains and to its margins where almost all the damage was recorded.
Badly hit were the towns of Edgecumbe, Te Teko, Kawerau, Matata and Thornton. Modified Mercalli Intensities (MM) of IX were reported in and around Edgecumbe, with possible instances of MM X.
In the USGS EXPO-CAT database it is estimated that during this earthquake 30,153 people were exposed to intensity VII or higher, of which around 14% were in rural areas.
It is reported that in Kawerau 40 houses were evacuated because of an unstable hill above them, and a higher number of people living in the Te Mahoe town, to the south of Matahina hydro dam was evacuated as precautionary measure.
No one was killed (although unfortunately one person died from a heart attack, possibly caused by the shock of the earthquake) and about 25 people were hospitalized.
The estimated overall economic loss (incl. insured losses and indirect losses) was ˜220 million USD (0.5% of the GDP of New Zealand in that period) and was largely accounted by damage to the commercial and especially industrial facilities in the area (˜80% of the direct economic loss).
The indirect losses represented about 16% of the overall losses, while insured losses accounted for 75%.
The majority of wood frame residences suffered damage to the chimneys or to roof and wall cladding and only few of them had serious structural damage, principally to foundation and rarely to frame.
Communities suffered loss of water, power supplies and sanitary drainage for long periods.
EM-DAT report a death caused by the earthquake (this was due to a heart attack)
˜16 out of the 4000 damaged dwellings suffered serious structural damage
These economic losses relate to 5.2 million US$ for repairs to the lifelines (Table 15); 3.4 million US$ in uninsured losses to houses and police stations; and 19 million US$ for repairs to schools, hospitals, roads, bridges and other public infrastructure (Table 14).
The insured losses (ca 162 million US$) are not included here.
Most of the indirect losses (92%) are related to economic effects (business interruption) and the rest is from welfare payments (8%).
In New Zealand all residential properties are insured by the Earthquake and War Damage Commission (now known as EQC).
However, the residential damage covered by insurance overstated what could realistically be attributed to the 1987 Edgecumbe earthquake. For example, chimneys were replaced by insurance but for many of them the cause of the damage was not the earthquake.
Butcher et al. (1998) give a detailed breakdown of the insured losses (in Table 14) by line of business as well as to business interruption effects (in Table 12).
Munich Re report much higher losses: 350 million US$ in overall economic losses, of which 270 million US$ in insured losses.