EARTHQUAKES Science Unit (Planet Earth & Beyond) Term 1 2011.

EARTHQUAKESScience Unit

(Planet Earth & Beyond)

Term 1 2011

LEARNING INTENTIONS

1. To identify features of the earth’s structure.

LEARNING INTENTIONS

2. To understand how natural forces cause

earthquakes.

LEARNING INTENTIONS

3. To explore the impact of earthquakes in NZ.

LEARNING INTENTIONS

4. To learn what to do before, during and after

an earthquake has struck.

THE EARTH’S STRUCTURE

WHY DO EARTHQUAKES HAPPEN?Plate Tectonics

New Zealand is right on the edges of two tectonic plates – the Australian and Pacific – and we get plenty of the action that goes with it!

Tectonic plates cause :

earthquakes, volcanoes, geothermal activity, tsunamis and landslides.

TECTONIC PLATES

Transform boundaries – The plates move past each other, but because of friction, they cannot just glide past each other so build up stress, which is released as an earthquake.

Divergent boundaries – The plates slide apart from each other and the space that this creates is filled with new crust from the magma formed below in the asthenosphere.

Convergent boundaries – The plates slide towards each other and moves underneath the other. This is a subduction zone, making deep marine trenches and volcanoes, some of the most explosive on earth.

At a subduction zone, two tectonic plates try to pass each other. Along faults, rocks grind past each other.Instead of sliding, some rocks lock together – but they are still being pushed, so they bend and stresses build up. Eventually, the pressure becomes too much, and the two sides of a fault jerk past each other. This releases stored energy as shock waves (called seismic waves) that travel out from the centre through the surrounding rock, sometimes to the other side of the world.

WHY DO EARTHQUAKES HAPPEN?

THE MAGNITUDE SCALE

Scientists use seismographs to measure when the seismic waves reach three different points, and they can work out where the focus and epicenter are. They also use the waves to work out the magnitude of the earthquake, normally measured on the Richter scale.

GeoNetSEISMOMETER

NETWORKThis map shows the

distribution of the main seismometers used to detect

earthquakes around New Zealand. During periods of seismic activity, temporary stations are also set up to gather more information.

EARTHQUAKES IN NEW ZEALANDAbout 14,000 earthquakes are recorded in and around

New Zealand every year. Fortunately, most of them

are too small for us to feel at the surface. However, many of us have felt the shake of

an earthquake, and there are some big ones that have

become part of New Zealand history.

EARTHQUAKES IN NEW ZEALANDJust offshore from the North Island, the Pacific Plate begins to descend beneath the continental crust on the Australian Plate. The descending plate presses against the overlying continental plate, causing the overlying plate to fracture and producing shallow earthquakes. Deep earthquakes occur in the oceanic crust that is being bent downward into the subsurface.

CHRISTCHURCH 2010

The Christchurch earthquake was a 7.1 magnitude earthquake which struck at 4:35 am on 4 September 2010.The quake caused widespread damage and several power outages in New Zealand's second largest city.

Two residents were seriously injured, one by a collapsing chimney and a second by flying glass. One person died of a heart attack suffered during the quake.

The earthquake's epicentre was 40 kilometres (25 mi) west of Christchurch, near the town of Darfield. The hypocentre was at a shallow depth of 10 km. A foreshock of roughly magnitude 5.8 hit five seconds before the main quake. The initial quake lasted about 40 seconds, and was felt widely across the South Island, and in the North Island as far north as New Plymouth.

About 100 faults and fault segments have been recognised around the region, some as close as 20 km to central Christchurch.

Aftershocks

THE COSTEarthquake Commission (EQC), private insurance and individual costs may reach as high as

$4 billion dollars !!!!!!

How do we prepare for an earthquake?

Develop a Household Emergency Plan.

Assemble and maintain your emergency survival items for your home as well as a portable getaway kit.

Practice Drop, Cover and Hold.

Identify safe places within your home, school or workplace.

How do we prepare for an earthquake?

1) Somewhere close to you, no more than a few steps or less than three metres away, to avoid injury from flying debris.

2) Under a strong table.

3) Next to an interior wall, away from windows that can shatter and cause injury and tall furniture that can fall on you.

What do we do during an earthquake?

•If you are inside a building, move no more than a few steps, drop, cover and hold. Stay indoors till the shaking stops and you are sure it is safe to exit. In most buildings in New Zealand you are safer if you stay where you are until the shaking stops.

•If you are outside, move no more than a few steps away from buildings, trees, streetlights and power lines, then drop, cover and hold.

•If you are at the beach or near the coast, drop, cover and hold then move to higher ground immediately in case a tsunami follows the quake.