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- Earthquake magnitude | geology | judsiohenphytat.tk
- Reappraisal of great historical earthquakes in the northern Chile and southern Peru seismic gaps
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Some of the major earthquakes within living memory have undoubtedly been the Kwanto Japan earthquake of which nearly destroyed Tokyo and Yokohama; the Tango Japan earthquake of ; the Idu Japan earthquake of ; the Hawkes Bay New Zealand earthquake of ; in India, the Bihar earthquake of and the Quetta earthquake of ; the Chilean earthquake of ; and the Turkish earthquake of All of these occurred in well established seismic zones where lighter earthquakes are by no means uncommon.
It is very rare for earthquakes even as great as the Baffin Bay earthquake of , to occur in places other than the usual zones. The Hawkes Bay earthquake of 3 February, , occurred without any warning at At Napier eyewitnesses saw buildings sway to an alarming extent, telegraph poles lean over at critical angles, cracks and fissures appear both in the walls of buildings and on the surface of streets, whilst control of motor cars became a matter of great difficulty owing to the peculiar nature of the Earth movement.
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Those who were not pinioned in buildings by the first shock had just reached the footpath when there came a second downward bump and many buildings collapsed. Owing to the scattering of fires in buildings numerous fires broke out in the town. About people were killed and many were injured. The Quetta earthquake of 31 May, , was one of the most destructive to human life of all known Indian earthquakes.
The disturbed area covered a band 70 miles long and 15 miles wide, running from Quetta through Mastung to midway between Mastung and Kalat. The Chilean earthquake of 24 January, , occurred at about It had an epicentre near Chillan which was practically wrecked. The disastrously affected area reached Parral in the north and Concepcion in the west, and upwards of 20, people were killed, many more being injured.
Such earthquakes as these have led to the formulation of schemes for earthquake insurance and to the better design of earthquake-proof buildings. The greatest earthquake ever recorded in Turkey happened at about 1. The loss of life was tremendous, estimates varying from the official figure of 23, dead and 7, injured to unofficial estimates of 45, killed and 20, injured. The high death roll was in part due to thick-walled mud houses of the locals collapsing on them whilst they were in bed.
This earthquake was recorded at observatories throughout the world on seismographs, many of which in effect are horizontal pendulums carrying a heavy inertia mass. The relative movement of the mass and the rest of the apparatus causes a pen at the end of the pendulum to write on paper fixed to a rotating drum the record of the earthquake.
Time marks are also made on the paper. I am indebted to Rev.
JP Rowland for the Stonyhurst record of the recent Turkish earthquake reproduced above. It was obtained with a Milne-Shaw seismograph registering optically with a galvanometer. The first waves to arrive have come through the body of the Earth. They are the P Primary or Push waves. Then come the S Secondary or Shake waves and finally the waves which have come round the surface of the Earth called L and M waves, for the knowledge of which we owe so much to Dr R Stoneley.
It will be noticed that for this particular earthquake the surface waves are extremely large.
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They exceeded the limits of registration at Kew and unhinged the seismographs at West Bromwich, Faenza Italy and some of the Swiss observatories. Knowing the speeds at which the P and S waves travel, it is possible by observing the time interval between the arrival of these at an observatory to estimate the distance of the epicentre of the shock from the station.
Doing the same for several observatories enables the epicentre to be determined approximately by drawing the arcual distances on a globe. Thence the original time of the earthquake may be determined. Greenwich Mean Time. Should the records of the earthquake exhibit large P and S waves and no L and M surface waves the earthquake is thought to have had a very deep focus. In that case waves peculiar to deep focus earthquakes are also discernible, and the arcual distance together with the initial time and depth of focus may be found by using special graphs prepared by Rev.
By identifying other waves seen on seismograms, students of seismology have drawn conclusions concerning the properties of the materials deep down in the Earth and the structure of the Earth. It appears that if we take the Earth to be a sphere of nearly 4, miles radius, the core has a radius of approximately 2, miles and is made of more dense material than the remainder.
Earthquake magnitude | geology | judsiohenphytat.tk
The core of the Earth appears to possess some of the properties of a liquid in that, according to general acceptance, it will not transmit S waves directly through the centre. Waves from an earthquake near to an observatory enable the crustal structure to be determined. Underneath the sedimentary surface rocks of variable thickness there appears to be from the surface downwards first a layer of granitic material estimated from 6. Artificial earthquakes caused by exploding charges of dynamite sunk in the ground have been used to determine the thickness of the ice-cap in Greenland and other places; to determine the position and size of salt domes in prospecting for oil; and to determine the geological structure including the depth of the sedimentary rocks in various parts of the world.
This work is done by portable seismographs and in the case of prospecting for oil has saved the companies thousands of pounds in avoiding unnecessary drilling. But will we ever be able to accurately predict these devastating incidents?
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Reappraisal of great historical earthquakes in the northern Chile and southern Peru seismic gaps
Press Releases. Reminder for Angelenos on Importance of Disaster Preparedness. The Red Cross offers these safety steps you should follow: During an earthquake, avoid moving around. Drop, cover and hold on. Try to protect your head and torso. If you are sitting at a desk or table, get under it. Otherwise, drop wherever you are. If you are in bed, stay there, curl up and hold on. Protect your head with a pillow. Stay indoors until the shaking stops and you are sure it is safe to exit.
You can find the maps of shaking from past earthquakes, see what earthquakes are happening around the world every day, and even get an email or text message sent to you every time there is an earthquake. This is just another reminder that new approaches to science can come from unexpected places.
Anyone — even you and your teachers, classmates, or families — can contribute valuable information to help scientists study important events like earthquakes.
Journal of Computational Science. Can Twitter Improve Earthquake Response? J Dent Res. Konkel, F , February 6. Tweets give USGS early warning on earthquakes. Citizens Contribute to Earthquake Science. The views expressed are those of the author s and are not necessarily those of Scientific American. Amanda Baker is a science communicator and outreach advocate. She has a geoscience PhD from Cornell University and has managed open-access, academic journals as well as the outreach journal Frontiers for Young Minds.