KEY POINTS:
A big undersea quake rocked Gisborne last night, the city mayor, Meng Foon, told residents to head for higher ground immediately if another quake struck, as no warning system was in place for "local" quakes. Thousands of residents had already fled.
* The quake hit at 8.55 with an estimated magnitude of 6.8 on the richter scale;
* Its epicentre was 50 km south-east of Gisborne and 40km deep in the Hikurangi Trough;
* It was felt widely, almost the full length of the country;
* Thousands of residents also headed for the hills on May 4 last year, after an overseas warning that a Tongan quake might trigger a tsunami;
* The Hikurangi subduction zone - an area of active faults - holds significant risk of a "local" tsunami;
* GNS called on December 20, 2005 for better computer modelling of the Hikurangi subduction zone as a potential tsunami trigger;
* NZ scientists record around 14,000 earthquakes a year, of which around 20 top 5.0 on the Richter scale; and
* A 6.2 magnitude quake in March 5 1966 damaged Gisborne's water and power supplies, and the main post office had to be demolished.
- NZPA
