Earthquakes

http://www.geonet.org.nz/earthquake/drums/

 

 

 

How New Zealand got here - animation of the past... (refresh the page to play it again)

 

 

 

http://www.gns.cri.nz/Home/Our-Science/Natural-Hazards/Research-Programmes/Plate-Tectonics-in-and-around-New-Zealand/Gondwana-animation

 

If you live for the next 4 million years the landscape is expected to change somewhat...

 

 

http://www.gns.cri.nz/static/download/def.mov

 

Looks like land values in northland may go up somewhat by that time ;)

About Magnitudes

...Firstly there was the richter scale...

---Local ("Richter") Magnitude (original defined by Richter - 1935)
ML = log A - log Ao

Because ML was not designed to to be applied to data with distances to the hypocenter of the earthquake greater than 600 km, its values become unreliable when the earthquake is larger than 7 and Richter's original method is no longer applied.

To overcome this shortcoming, Gutenberg and Richter later developed a magnitude scale based on surface waves, surface wave magnitude MS; and another based on body waves, body wave magnitude mb. MS and mb can still saturate when the earthquake is big enough.

---Surface Wave Magnitude
Ms = log (A/T) + 1.66 log D + 3.3
---Compressional Body Wave (P-wave) Magnitude
Mb = log (A/T) +Q(D,h)


...Then came Mw ...
The moment magnitude scale is used to measure the size of earthquakes in terms of the energy released. The magnitude is based on the seismic moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of the area that slipped. The scale was developed in the 1970s to succeed the 1930s-era Richter magnitude scale (ML). Even though the formulæ are different, the new scale retains the familiar continuum of magnitude values defined by the older one. The MMS is now the scale used to estimate magnitudes for all modern large earthquakes by the United States Geological Survey.

---*Moment Magnitude
Mw = (2/3) log Mo - 10.7


USGS usually uses the Mw scale to report magnitudes - although i have seen them use the Mb sometimes too


...Then there's NZ - Geonet say...
The magnitudes assigned to local earthquakes are intended to be the values of ML as originally defined by C.F. Richter ..., but his procedure for performing the magnitude calculation at other than the standard distance of 100 km has been modified, to take account of the observed characteristics of energy propagation in New Zealand, including the effect of focal


And they use the following formulas instead

---For stations more than 100 km away from the epicentre
A = A0 R-N exp ( - α R )

---For stations closer than 100 km to the epicentre
MA = log10 A + 1.0 log10 R + 0.0029 R + K


which is why when you look here:
http://earthquake.usgs.gov/earthquakes/eqinthenews/2011/usb0001igm/
it says 6.1
but if you look here:
http://geonet.org.nz/earthquake/quakes/3468575g.html
it says 6.3

...So remember to add a couple of points to all the overseas shakes you see in order to compage them with the ones you feel in NZ :)

references...
http://www.geonet.org.nz/resources/earthquake/hypocentre-derivation.html
http://neic.usgs.gov/neis/phase_data/mag_formulas.html

all that maths make ya brain hurt?  did mine :|

---

*** Google Earth and Geonet Feeds ***

First - if you dont have google earth - download and install it...

next - open google earth - and add a feed

find the left hand places panel with the "My Places" on it

right click it -> add -> network link

choose any name you like for the link - mine are named by month and year

Paste the following link into the link box

http://magma.geonet.org.nz/services/quake/kml/2.2/search?sta
rtDate=2011-04-01&endDate=2011-04-30

Adjust the dates in the link for the month you want - note they are in yyyy-mm-dd format

press ok button

to show the quakes on your map...

make sure the tick is ticked next to the folder in your my places list

when it is, a timeline thingy will appear top left of the map...
it has 2 pull handles on it - usually they start out together
- pull the top one across to the right of the slider
- then pull the bottom one, on the left of it, back to the left a bit
this makes a timeframe - so you can show all the quakes for however many days you like

when you have a gap set - you can play the sequence...
pull the right hand handle back to the left side of the slider - and press the play button above the slider

you can add more months to your my places folders by adding another network link and adjusting the dates again - then you can tick as many months as you like at once and play them in sequence

for the current month thats not finished yet - put in the whole month worth for the link (like above) then each time you want to look - right click on that month folder and pick "refresh" - it will then fetch any new quakes since last time you looked and add them for you...

more info on setting your link here:
http://geonet.org.nz/resources/earthquake/quake-web-services.html