For further study: WinQuake software and copy of seed file for IRIS/USGS seismographic stations and for the HKT station.

Learning Experience – 1A. Tutorial on understanding the origin and types of seismic wave

Time Frame - 20 minutes

Materials (tutorials 1A - 1C)

• Globe
• Hockey (HKT) seismograms of the March 20, 1999 Andreanof Islands earthquake.
• Traveltime curves
• Slinky (coiled spring)
• A small piece of string or a compass (for measuring distances on the map).
• World maps with both seismographic stations and an earthquake epicenter marked on one and only the seismographic stations on the other.
• Computer workstation
• Seismic Eruption and Seismic Waves software (available from http://www.geol.binghamton.edu/faculty/jones/jones.html ).
• Web browser with some "Virtual Earthquake" and PEPP websites bookmarked
  http://vcourseware4.calstatela.edu/VirtualEarthquake/VQuakeIntro.html
  http://lasker.princeton.edu/index.shtml

Advanced Preparation

The presenter/teacher will need to explain the terms/concepts shown in italics.

Procedure

1. The presenter/teacher will introduce concepts using a globe and a slinky. He or she will ask participants/students if they can think of examples of "imaging" something with sound (bats, sonograms, sonar, etc.). The presenter/teacher will point out the differences between imaging the Earth with earthquakes and these other examples: the unknown source (earthquake) locations. Before we can image the Earth we need to have accurate estimates of where and when each earthquake occurred.
2. The presenter/teacher will pass out paper copies of HKT data for the March 20, 1999 Andreanof Islands event (Figure 1). Do you see any patterns? State that the objective of this lesson is that patterns in the seismograms will be both clear and meaningful by the end of the lesson.
3. The presenter/teacher will explain compressional and shear wave motions (use slinky to demonstrate motions), surface waves and the paths of important phases (P, PP, PcP, S, SS, ScS). The presenter/teacher will also explain how distance is measured in terms of an angle at the center of the Earth (Figure 2).
4. Participants/students will explore the Seismic Waves software (available from http://www.geol.binghamton.edu/faculty/jones/jones.html).

• Start with tutorial mode.

• Choose South America event.

• Cross-section (lower right): Point out the types of wave motion (compresional, shear, surface waves), relative speeds of travel, different paths. Describe the major boundaries at Earth’s surface, core-mantle, and inner core-outer core. Waves change and are reflected by (bounce off) these boundaries.

• World map view (lower left): Waves propagating across the Earth. Different wave motions travel at different speeds.

• Seismograms (top): Waves arriving at the different stations around the world are recorded on seismograms, which are graphs of the Earth’s motion as a function of time.

• Allow tutorial to run through several events while describing the wave propagation again. Allow participants to explore the program on their own for 5-10 minutes.

5. Look at figure of traveltimes (Figure 3). Once we have identified the arrivals of the various waves and have found an earthquake’s epicenter, we can plot the time it takes each wave to travel from the epicenter to each seismographic station. With many earthquake-station combinations, the traveltimes start to form patterns (lines). See Figure 4.

Learning Experience 1B. Tutorial for finding epicenter location and magnitude

Time Frame - 20 minutes

Procedure

Participants/students will carry out the "Virtual Earthquake" earthquake location Web-based tutorial. Anyone finishing early should look at the depth calculation discussion on the PEPP website.

Learning Experience 1C. Web-based tutorial on understanding earthquakes in terms of plate tectonics.

Participants/students will use the Seismic Eruption software (available from http://www.geol.binghamton.edu/faculty/jones/jones.html) to plot the locations of volcanoes and earthquakes around the world.

Time Frame - 20 minutes

Procedure

1. Start the tutorial on your computer.
2. Choose the world map and watch the earthquakes and volcanoes as they are plotted around the world. What patterns do the earthquake locations make? Where do earthquakes and volcanoes tend to occur?
3. Use the program to illustrate the depth of earthquakes in the Cook Inlet subduction zone. What causes these earthquakes? (The motions described by plate tectonics require new crust to be created and old crust to be subducted.)
4. Point out New Georgia Islands (orientation for later lesson).

Formative Assessment of A, B and C

• The presenters/teachers will ask questions of participants/students while they explore the tutorials to ensure that they understand the concepts and how to use the software.

• Use WinQuake to plot data from the IRIS/USGS and/or HKT seed files. WinQuake tries to automatically plot the arrival times of P and S and use them to compute distance.

Summative Assessment 

This activity is designed to determine whether the participants/teachers have understood the material contained in the tutorial sufficiently well to apply it to a real problem.

Time Frame - one hour

Procedure

1. Return to the paper copies of HKT (east-west, north-south, vertical) data (Figure 1) and try to identify the arrival times of P, PP, S, and surface waves.

2. Characterize these waves in terms of relative arrival times, frequency content, amplitudes, and wave motion.

3. Use these numbers and the traveltime curves to estimate the earthquake's distance from Hockley. Was the earthquake shallow or deep?  How do you know?

4. Look at Figure 5, map with station locations but no earthquake epicenter. Look at Figure 6 which shows a record of sections with fixed start time. If we have data from all these stations (which are now available via the Internet), how should we arrange the data in order to reveal patterns? (Once we know where the earthquake is located we can arrange them by increasing distance.)

5. Assuming you have found the distance to be 62º from HKT, 34º from KIP, 55º from SFJ, and 30º from YAK, approximately where is the earthquake's epicenter?

6. Look at map with epicenter marked (Figure 7).

7. We can then sort the seismograms shown in Figure 6 by distance from the epicenter, which reveals the arrivals of the various phases (marked by traveltime curves superimposed on the seismogram record section).

EXTENSIONS

Field trip to a working seismic station (Hockley or Junction) or to UTIG may be arranged.

UTIG operates and maintains the Hockley Seismic Station. The station has been given the station code HKT for use with Global Seismic Network (GSN), operated by the Incorporated Research Institutions for Seismology (IRIS). The Hockley station is also a cooperating member of the United States National Seismic Network (USNSN) maintained by the USGS. Data acquired from the system is forwarded to GSN.

The Hockley seismometer is located in a chamber 470 meters below the surface in an active salt mine owned by United Salt Corporation. Locating the instrument within a salt dome reduces the noise from human activity that affects instruments on the surface. The seismometer consists of three Streckeisen STS-1 sensors oriented vertically, north-south, and east-west, mounted on a concrete slab, and kept in evacuated containers. The seismic sensors feed a signal directly to the data acquisition (DA) unit. The heart of the DA is a Motorola VME-147s computer running OS-9 system software. A fiber optic cable connects the DA to VSAT communications hardware, a GPS clock, and a dial-up modem on the surface. Using the VSAT link, the data stream travels to the National Earthquake Information Center (NEIC) in Golden, Colorado, where the USNSN monitors national earthquake activity. The NEIC then transmits the seismometer data via satellite to the data processing (DP) system located in the main computer room at UTIG in Austin.

The DP consists of a Motorola VME-147S computer running OS-9 system software. Hockley data are stored on tapes and then sent to the IRIS Data Collection Center for further processing and archival at the IRIS Data Management Center in Seattle, Washington. Each archived earthquake includes the hypocenter coordinates, the date and time of the earthquake, a reported magnitude estimate, a three-component seismogram, and lastly the body wave phase arrival times. Body wave phase arrivals are named according to the ray path they take.