Jolt and shake Earthquakes produce several types of waves that move through the earth at different speeds. Primary (or pressure) waves are the fastest and are thus the first to be felt. They are similar to sound waves and may produce a distinct jolt, rattling windows and dishes. Secondary waves (or shear waves) travel more slowly. They shake the ground both up and down and from side to side, and do the most damage to man-made structures. You may thus feel two distinct tremors from an earthquake, as the primary and then secondary waves arrive.
11:42 AM
23.4.04
Totara Park - suburb on a faultline Part of Totara Park, a suburb of Upper Hutt, has been built directly over the Wellington Fault. The layout of the streets in the suburb has been specially designed to minimize earthquake damage. One street has been aligned so the fault line runs down the middle of the street under a grassed centre berm. No house is closer to the fault than 20 metres. Very few service lines, such as water, gas and sewerage, cross the fault, and those that do have flexible joints to withstand movement. 1:52 PM
16.4.04
Solar flares and power systems
Solar flares and emissions of material from the Sun’s corona can cause “geomagnetic storms” - powerful disturbances to Earth’s magnetic field. These storms can affect the transmission of electricity along power lines and transformers at power stations. On 23 March 1989, Hydro-Quebec had a 9-hour power blackout affecting 9 million people. The cause was a strong geomagnetic storm.
2:20 PM
8.4.04
The average annual cost of damage from flooding in New Zealand exceeds the average annual cost of damage from earthquakes and volcanoes put together. Damaging storms occur much more frequently than damaging earthquakes and volcanic eruptions.
The Otira Zigzag
State Highway 73 crosses the main divide of the Southern Alps in Arthur’s Pass National Park. At a section known as the Zigzag, the highway descended across a series of prehistoric landslides. Sections of the road periodically crumbled away as the Otira River cut into the base of the slope. Rock falls from the cliffs above the road sometimes bombarded traffic. This hazardous section of highway was finally abandoned when the 440-metre-long Otira Viaduct opened in November 1999.
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