Why the 2011 Christchurch earthquake is considered an aftershock. The magnitude 7.1 earthquake that struck the Canterbury region on 4 September 2010 was caused by the rupture of a fault network deep beneath the Canterbury Plains. The rupture started at 10 km below the surface, and then broke open a 24 kilometre rent across the surface of the plains. In the days following the quake, geologists from the University of Canterbury and GNS Science mapped the location of the surface rent, which extended from Greendale to near Rolleston, and named it the Greendale Fault. Part of the energy of the main earthquake, however, was contributed by rupture along branching faults near the western end of the Greendale Fault, faults that didn’t reach the surface.
Graphic showing location of main shock, aftershocks above magnitude 3, and fault ruptures in Canterbury. These aftershocks usually continue for many months after a major earthquake. Over many months a cloud of aftershocks has developed, indicating a network of subsurface faults. Christchurch quake was aftershock from 2010, scientists say | World news. The earthquake that brought death and destruction to Christchurch on Tuesday was almost certainly an aftershock of a larger quake that rocked New Zealand on 3 September last year.
But while last year's earthquake was more energetic, it struck in the early hours of the morning, some 48km outside the city. The quake that hit on Tuesday was more devastating for several reasons: it was shallower, much closer to Christchurch and arrived in the middle of local lunchtime at 12.51pm. Earthquakes are not rare in New Zealand. The islands are shaken by noticeable tremors on average twice every three days. Seismologists at the US Geological Survey have recorded at least six earthquakes of magnitude five or more since September's magnitude 7 incident. Tuesday's earthquake was recorded at magnitude 6.3, or roughly 11 times weaker, but it was enough to raze buildings already damaged by the previous earthquake and later aftershocks. GeoNet: M 6.2 Christchurch Tue, Feb 22 2011.
The city had been comparatively lucky with both the location and timing of the earlier magnitude 7.1 Darfield (Canterbury) earthquake; the location of this one however - within 10 km of the city and at a shallow depth of 5 km - during the middle of a working day resulted in destruction, injuries and deaths. Magnitude: ML 6.3Casualties: 185 deaths Aftershock detection GeoNet staff deployed portable earthquake recorders to collect information on the rich aftershock sequence of the earthquake. Earthquake data from the portable instruments are used in conjunction with data from permanent GeoNet monitoring stations and portable instruments that had remained deployed following the M7.1 Darfield earthquake. In total, 6 short-period seismometers and 4 strong-motion accelerometers were placed around the outskirts of Christchurch. Focal Mechanisms Focal mechanisms or fault plane solutions show the fault and direction of slip.
Landslides and Rockfalls Portable GPS deployment in Clifton and Redcliffs. Learning from the Christchurch Earthquakes - Google Slides. The tectonic forces that are shredding New Zealand. By Wendy Zukerman This week the New Zealand city of Christchurch felt the force of a 6.3-magnitude earthquake. The quake came just five months after an even larger one struck 40 kilometres west of Christchurch, near the town of Darfield. In fact New Zealand experiences around 14,000 tremors each year, although most are too small to be felt.
They are a sign of the tectonic processes that are gradually shredding the country. Why is New Zealand so prone to earthquakes? Which areas are most vulnerable? The relatively low-density continental crust of the North Island, which sits on the Australian plate, is forcing the dense oceanic crust on the Pacific plate beneath it in a process called subduction. Advertisement Something similar is occurring to the south-west of South Island. In between, the continental crust on the Pacific and Australian plates slide past one another on South Island, creating a conservative plate margin where crust is neither created nor destroyed. More on these topics: How does a seismograph work? What is the Richter scale?" A seismograph is the device that scientists use to measure earthquakes.
The goal of a seismograph is to accurately record the motion of the ground during a quake. If you live in a city, you may have noticed that buildings sometimes shake when a big truck or a subway train rolls by. Good seismographs are therefore isolated and connected to bedrock to prevent this sort of "data pollution. " The main problem that must be solved in creating a seismograph is that when the ground shakes, so does the instrument. The Richter scale is a standard scale used to compare earthquakes. How Seismographs Work. Scientists who weren't in Chile during this morning's aftershocks nevertheless knew the moment the rumbling started, thanks to a global network of quake-detecting instruments called seismographs. Seismographs are securely mounted to the surface of the Earth, so when the ground starts shaking, the instrument's case moves.
What doesn't move, however, is a suspended mass inside the seismograph, called the seismometer. During an earthquake, the seismometer remains still while the case around it moves with the ground shaking. Traditionally, the suspended mass was a pendulum, but most modern seismometers work electromagnetically. A large permanent magnet is used for the mass and the outside case contains numerous coils of fine wire. Movements of the magnet relative to the case generate small electric signals in the wire, which can be sent to a computer or recorded onto paper to create a seismogram. Seismographs can detect quakes that are too small for humans to feel.
Seismic waves. When an earthquake occurs, the shockwaves of released energy that shake the Earth and temporarily turn soft deposits, such as clay, into jelly (liquefaction) are called seismic waves, from the Greek ‘seismos’ meaning ‘earthquake’. Seismic waves are usually generated by movements of the Earth’s tectonic plates but may also be caused by explosions, volcanoes and landslides.
Seismologists use seismographs to record the amount of time it takes seismic waves to travel through different layers of the Earth. As the waves travel through different densities and stiffness, the waves can be refracted and reflected. Because of the different behaviour of waves in different materials, seismologists can deduce the type of material the waves are travelling through.
The results can provide a snapshot of the Earth’s internal structure and help us to locate and understand fault planes and the stresses and strains acting on them. Types of seismic waves P-waves S-waves Surface waves Metadata. Why the 2011 Christchurch earthquake is considered an aftershock. Canterbury Earthquakes Information Paper.
Liquefaction demonstrated – Historic earthquakes. Seismic Waves in Christchurch. Canterbury earthquakes. An earthquake near Christchurch in September 2010 started a chain of events still being felt over 2 years later. It caused extensive damage to property, and aftershocks also caused injury and loss of life as well as lasting social upheaval. The events around Canterbury are examples of common geological phenomena associated with earthquakes. They are important to study because they are potential hazards to human life and property. Fault movement Early on 4 September 2010, a magnitude 7.1 earthquake occurred on an unrecorded fault near Darfield, 40 km west of Christchurch and just 10 km below the surface.
Seconds later, the Greendale Fault just to the south ruptured. One result of this readjustment was a damaging aftershock (magnitude 6.3) on 22 February 2011, when a fault ruptured very close to Christchurch. 3 shocks of magnitude 6–6.9 54 of magnitude 5–5.9 431 of magnitude 4–4.9 over 3000 of magnitude 3–3.9 thousands of smaller tremors. Ground movement Liquefaction Landslides and rockfalls. Seismic Waves" This content is not compatible on this device. Click the play button to start the earthquake. When P and S waves reach the earth's surface, they form L waves. The most intense L waves radiate out from the epicenter. When you toss a pebble into a pond, it creates radiating waves in the water. There are several types of seismic waves. Primary waves (or P waves) are the fastest moving waves, traveling at 1 to 5 miles per second (1.6 to 8 kilometers per second).
Secondary waves (also called shear waves, or S waves) are another type of body wave. Unlike body waves, surface waves (also known as long waves, or simply L waves) move along the surface of the Earth. How do scientists calculate the origin of an earthquake by detecting these different waves? Christchurch earthquake kills 185. On Tuesday 22 February 2011 at 12.51 p.m. Christchurch was badly damaged by a magnitude 6.3 earthquake, which killed 185* people and injured several thousand. The earthquake’s epicentre was near Lyttelton, just 10 km south-east of Christchurch’s central business district. The earthquake occurred nearly six months after the 4 September 2010 earthquake, but is considered to be an aftershock of the earlier quake. The earthquake occurred at lunchtime, when many people were on the city streets.
Although not as powerful as the magnitude 7.1 earthquake on 4 September 2010, this earthquake occurred on a fault line that was shallow and close to the city, so the shaking was particularly destructive. The earthquake brought down many buildings that had been damaged in September 2010, especially older brick and mortar buildings. Liquefaction was much more extensive than in the September 2010 earthquake. Text adapted from Te Ara with acknowledgements to GeoNet and GNS Science. Liquefaction. Liquefaction is a process that temporarily turns firm ground into a liquid. During the Canterbury earthquakes of September 2010 and February 2011, liquefaction caused silt and fine sand to boil up and bury streets and gardens and caused buildings and vehicles to sink. This was a new phenomenon for most New Zealanders, yet it has been a feature during earthquakes throughout this country’s history. There is evidence of liquefaction in most of the largest earthquakes since the 1840s, including the Hawke’s Bay quake of 1931.
Next time you are on a sandy beach, walk across some wet sand a little back from the water’s edge. It’s firm walking, though you might leave footprints. Causes of liquefaction Over thousands of years, rivers deposit layers of silt and sand in many places, especially in low-lying ground and near the coast. Severe shaking in an earthquake puts pressure on the silt and water particles in these waterlogged layers, turning once firm sediment into a liquid. Nature of Science.