Tuesday, March 22, 2011

Earthquakes - Exploring our website data - Part two.

Quake Drums : 101

The most common means of displaying seismic monitoring data is called a seismogram. Traditionally these were drawn by ink on paper, but today are usually created by computers using digital data.
You read a seismogram like you are reading these words; the earliest time is at the top left and then goes along the line to the end and then starts at the left of the next line. The top-left is therefore the oldest data and the bottom-right the most recent. All of our drums cover a 24-hour period.

The drums on the GeoNet website do not display 'real-time' data as the volume of data required to be sent across the internet is too great.  Instead, each seismogram is produced every 5 minutes and the web page updated as each new image becomes available.

An earthquake typically is a signal that is much larger then the normal background. A nearby earthquake usually has a very sudden onset and decays away relatively quickly (usually less than 5 minutes). With a more distant earthquake you may be able to see both the P- and S-waves and the earthquake decays away more slowly. Because of the limited resolution of the seismograms you cannot always see the both the P- and S-waves, especially for nearby earthquakes.

The traces are coloured in dark blue and purple so it is easier to see which data corresponds to each line. A seismogram is coloured red if is clipped, ie. the largest parts of the signal are not shown. If this was not done then a large earthquake would obscure much of the seismogram from view. In other words, if the signal is red the real size is larger than is shown on the seismogram.

Seismograms are not all at the same scale. This is as some sites are noisier than others and tend to be plotted at a scale that shows a smaller signal (these sites have a larger scale number). To plot these sites at the same scale as nearby, quieter sites would result in a seismogram completely blue (or red) and would show no useful information.

The seismometers that we use are very sensitive instruments and can sometimes be triggered by unrelated phenomena like weather, traffic or movement of livestock.

NOTE: Not all earthquakes that are widely recorded on these traces are felt by people.



Monday, March 14, 2011

Earthquakes - Exploring our website data - Part one.

We quite often get queries (via email and facebook) wondering on how many earthquakes a particular area gets, and 'was there an earthquake yesterday' etc.  and more recently we have had lots of questions regarding Christchurch!   I will do a series of posts on how to find and use the data within our website which will hopefully help you answer those questions now and in the future.

You all know we get a large amount of earthquakes in New Zealand every year (we locate over 15,000!) we only put the larger/more widely felt earthquakes onto our 'recent quakes' page (or else it would be chocka!)  Now we aren't hiding anything, you can access all of our data via our website!   We have heaps of cool things for you to look at on our website via the 'Resources' tab, here are a couple ..

Quake Search  CLICK HERE
This lets you search in a particular area, date and size of earthquake.
1 - Draw a box around the area of NZ you are interested in. (or you can put in the coordinates)
2 - Select the time frame - note. UTC = Universal time = at the moment is 13hrs behind NZ time.
3 - If you are interested in quakes of a certain size, put the magnitude in here.
4 - Output: you can choose * CSV= spreadsheet, Here you get all the guff -  numbers, mag, depth etc
     *Map (with or without towns) and * KML - which will open up in Google Earth.

Here is an example of all of the earthquakes in Canterbury from March 1st until the 14th:

Wednesday, March 2, 2011

Christchurch Landslide Response ~ Site 2

The team are now at Clifton and about to install equipment on a property with very large cracks in the lawn as shown in the pics below:

In this photo you can see the temporary gps equipment set up in the background.

Andrew connecting the gps.

Christchurch Landslide Response ~ Site 1

Todd and Andrew and busy installing the first of the gps sites. I spoke with Andrew this afternoon and he said this site is at Redcliffs above the slip that fell onto a school.

 Todd digging a hole next to the temporary gps installed last week.

And Todd again, tinkering with the new semi-permanent gps equipment almost ready to go.

ShakeNZ Animation of the 22 Feb 2011 Christchurch Earthquake

Tuesday, March 1, 2011

Christchurch Landslide Response

Two of our team (Andrew and Todd) are gearing up to head down to Christchurch for GNS Engineering Geologist and landslide wizz Chris Massey.

The team are going to install two precision gps instruments (pictured right) at Sumner and Redcliffs landslides, to monitor potential land movement.  

More info to come tomorrow!