Using the Network

Earthquakes in New York?

• earthquakes detected by LCSN in northeast (1995-1998)
• Large historical events near New York City
• April 20, 2000 near Newcomb, NY (magnitude 3.8)

Lamont-Cooperative Seismic Network (LCSN)

• LCSN monitors seismic activity in NY,NJ,DE,VT,...
• Purpose:
  • detect and locate seismic events in northeast
  • assess seismic hazard near population centers
  • illuminate Earth structure under the region
• list of current seismic stations
• The LCSN network records:
  • local events. example - Temiskaming, QC, January 1, 2000
  • regional events. example - Vancouver Island, BC, April 30, 2000
  • global events. example - Sulawesi, Indonesia, May 4, 2000
• ACC station: details, location
• BRNJ station: details
• Parts of a seismic station
• how the network is assembled

Intro to WebSeis

• Mission: to provide easy access to up-to-the-minute seismic information
  • easy enough anyone to browse and understand
  • with basic tools for manipulating
  • options for research-oriented users
• see current data (WebSeis main page)
• day selection: 24-hour view of each day (in Greenwich mean time)
• station selection: PAL, ACC, ...
• frequency selection:
  • "tunes" a seismogram to a particular type of signal
  • minimizes Earth noise (background vibrations in Earth partially due to weather and ocean waves)
  • Filtering tutorial

• components:
  • ground vibrates in 3 dimensions, each is recorded separately
  • compressional (P) and rayleigh waves, typically more clear on vertical component (Z)
  • shear (S) and love waves are often more clear on horizontal components (E & N)
• Advanced features: creating and downloading your own seismograms
  • select ZOOM button, SHORT HELP button offers quick guidance
  • 1st use DATA SETTING button to select a piece of data
  • FILTER SETTING, OUTPUT SETTING, PLOT SETTING to custom tailor seismogram
  • EVENT INFO adds earthquake information from catalogue
  • use CLEAN UP when finished

What WebSeis records

• Seismometers record anything that makes the ground shake
• events seen on seismograms include:
  • earthquakes: small local events, large global events
  • explosions: mining blasts, nuclear weapons tests, ...
  • storms: wind (swaying trees) near the seismometer, large ocean waves, ...
  • human noise: nearby people, vehicles, industrial sites, utility pipes and wires, ...
  • ... and occasionally: volcanic eruptions, landslides, avalanches, meteor impacts, ...
• earthquakes, storms and explosion (mostly from mines and quarries) account for most seismic activity
• each type of signal is distinguishable with practice

Using WebSeis to identify earthquakes
(for explanation of terms, see the seismology primer page)

• select a day to examine (select settings and click "submit")
• you may find the long-period or long-periodx5 setting makes events more noticeable
• if you are not sure if a feature is an earthquake, try scanning the seismogram gallery for similar signals
• estimate time of earthquake
  • first signals on seismogram may be many minutes after event
  • almost no delay for local events, 20+ minutes for events on other side of world
• estimate distance to earthquake
  • if the shaking lasts less than a minute or two it is very local
  • if it lasts 5-20 minutes it may be nearby (Mexico, Alaska, California, ...)
  • if it lasts half hour or more it is likely very far away (South Pacific, Asia, ...)
• check bulletins for earthquakes which have been located
  • Events typically show up on the NEIC bulletin within a few hours of event
  • NEIC bulletin is national and may not show smaller local events
  • LCSN bulletin will show smaller events but may not list them as quickly
• identify phases
  • identifying seismic phases is not hard but takes some practice, use gallery for examples
  • try to identify first arriving P phase on vertical component a S on horizontal components
  • time separating P and S can be sued to estimate the distance to an earthquake in degrees
    • distance = (S-P time in minutes - 2) * 10
    • example: S arrives 8 minutes after P. Distance = (8 - 2) * 10 = 60 degrees
  • other paths through the Earth can be identified using guidelines in seismology primer