The AS-1 Seismograph – Operation, Filtering, S-P Distance Calculation, and Ideas for Classroom Use 1

 

L. Braile, November, 2002;

Updated November, 2004

braile@purdue.edu

http://web.ics.purdue.edu/~braile

       

 

 

Examples of Recorded Seismograms and Filtering of Seismograms:  The AS-1 seismometer (Figure 1) has a natural period of oscillation of about 1 s.  To make the seismometer more useful for recording local as well as distant earthquakes, the amplifier unit supplied with the AS-1 uses strong filtering to enhance the long period (greater than 10 s period) response of the instrument.  The combined response of the seismograph is more broadband and can record signals ranging from about 30 s period to 2 Hz (0.5 s period).  Local and regional (within about 1200 km or 10 degrees distance from the seismograph location) earthquake seismograms are usually dominated by short period (near 1 s period) energy.  Teleseismic (distant earthquakes, 10 to 180 degrees) recordings usually consist of lower frequency (longer period) energy and often have prominent surface wave arrivals of 12 – 30 s period.  Microseisms are a nearly universal source of ground noise in seismic recording and have periods of about 3 – 8 s.  Because this period range is amplified strongly by the AS-1 seismograph, filtering of the records is often desirable to enhance the earthquake signals.  A useful filter for local and regional events (short period) is a bandpass filter with frequency cutoffs of 0.5 Hz to 3 Hz (frequency in cycles per second, or Hertz, is equivalent to 1/Period in seconds, so these cutoffs are the same as 2 s period and 0.333 s period; in the AmaSeis control menu, after the seismogram is selected or extracted, enter the two frequencies, lowest frequency is cutoff one, highest frequency is cutoff two).  An example of use of a short period filter is shown in Figures 2 and 3 for an earthquake that was located 2.63 degrees (~292 km) from the station.

 

 

 

 

[1]                               Last modified November 21, 2004

The web page for this document is:

http://web.ics.purdue.edu/~braile/edumod/as1mag/as1mag2.htm.     

Partial funding for this development provided by IRIS and the National Science Foundation.

ã Copyright 2002-4.  L. Braile.  Permission granted for reproduction for non-commercial uses.

 

Figure 1.  The AS-1 seismometer showing the main components of the instrument.  The AS-1 is a vertical component seismometer.  Up and down motions of the ground, and therefore of the base and frame of the seismometer, cause the coil to move relative to the magnet that is suspended by the spring and boom assembly.  The mass of the seismometer, consisting primarily of the magnet and the washers, tends to remain steady because of inertia when the base moves.  The motion of the coil relative to the magnet generates a small current in the coil.  The current is amplified and digitized by an amplifier unit (not shown) and connected to the computer for recording and display.  The damping (using oil in the container and a washer mounted to a bolt extending downward from the boom into the oil) reduces the tendency for the mass and spring system to oscillate for long duration from a single source of ground motion (arrival of seismic waves at the location).

 

 

 

 

 

 

 

 

Figure 2.  AS-1 seismogram recorded at West Lafayette, Indiana from an earthquake located near Evansville, Indiana, December 7, 2000.  The earthquake epicenter was about 292 km away from the seismograph and had a magnitude of about 3.9 (mbLg).  Microseisms of about 3-6 second period are visible before the first arrival (the compressional or P wave) that is located at about 1.1 minutes (relative time).  The S (Shear) wave and surface waves are the largest arrivals following the P wave.

 

Figure 3.  Seismogram for the Evansville earthquake (Figure 2) after filtering (0.5 – 3 Hz cutoffs) to enhance the high frequency energy of the earthquake signal.  The P, and S and surface wave arrivals are recognized partly by the frequency contrast and are slightly enhanced, as compared to the background microseism noise and the unfiltered seismogram shown in Figure 2, on the filtered seismogram.

 

For teleseismic or distant earthquakes, lower frequency filtering often enhances the seismogram, especially the surface wave arrivals that are prominent for shallow focal depth (0 – 70 km depth) earthquakes.  Suggested filter cutoffs for lower frequency (longer period) signal enhancement are 0.01 Hz (cutoff one) to 0.2 Hz (cutoff two), equivalent to a 100 s to 5 s period range.  Because the seismograph has very low response at very low frequencies, the lowest frequency cutoff (0.01 Hz) is intended primarily to avoid amplitude distortion and offset of the zero level of the trace that is sometimes caused by filtering the extracted trace.  An example of the advantages of filtering seismograms to enhance the long period energy is shown in Figures 4, 5 and 6.  Figure 4 is the AmaSeis screen display for a 24 hour record (each horizontal trace is one hour long; the display is designed to look like the familiar drum recording on paper; hours scale is along the left side; minutes scale is at the bottom) including an earthquake that occurred at 11:41:47.9 (Greenwich Mean Time, GMT), August 9, 2000, in Michoacan, Mexico.  The event had a magnitude of 6.5 (surface wave magnitude, MS) and was located about 25.96 degrees (2887 km) from the seismograph at West Lafayette, Indiana.  The extracted seismogram (Figure 5) shows a close-up view of the earthquake signal.

 

Figure 4.  AS-1 seismograph recording for August 9, 2000, Michoacan earthquake.

 

Figure 5.  Extracted seismogram for the Michoacan earthquake.  Amplitude scale is in count or digital units.

 

The filtered seismogram (Figure 6) enhances the main arrivals and makes it much easier to determine arrival times.   Filtering using the control menu in AmaSeis can be performed more than once to further enhance the frequency range of interest.

 

 

Figure 6.  Extracted seismogram for the Michoacan earthquake after bandpass filtering (0.0001 Hz and 0.1 Hz cutoff frequencies) to enhance the long period (10,000 – 10 s) energy.  The P wave arrival (the first arriving energy is at about 3 minutes, relative time, followed about 40 s later by the PP arrival.  The PP phase is a P wave that reflects from the Earth’s surface once near the halfway distance between the epicenter and the seismograph station.  The S (shear) wave arrives at about 7.5 minutes and is visible partly because of the frequency change (lower frequencies often characterize the shear waves).  Prominent surface waves (Rayleigh waves) are visible at about 14 – 15 minutes relative time. 

 

S-P Distance Calculation:  The AmaSeis software includes a useful tool for determining the epicenter-to-station distance from the S-P arrival time difference on seismograms.  For AS-1 seismograms extracted from a 24 hour record or saved as SAC files, or for SAC format seismograms downloaded from the internet, the AmaSeis arrival time picking tool can be used to mark the interpreted arrival times of the P and S waves (Figure 7).  Then, by selecting the travel time curve tool, the seismogram is displayed on standard travel time curves.  By moving the seismogram on the screen, the interpreted P and S times can be aligned with the arrivals on the travel time curves (Figure 8).  The S-P times can also be analyzed using standard travel time curves (Bolt, 1993, p 134; or from the internet at http://lasker.princeton.edu/index.shtml). Once aligned, the epicenter to station distance is determined and displayed.

 

Figure 7.  Vertical component seismogram from GSN station KIP for the September 30, 1999 Oaxaca earthquake.  The SAC file was downloaded using the IRIS WILBER tool.  The seismogram was displayed using AmaSeis and the P and S arrival times (vertical red lines) picked. 

 

Figure 8.  KIP seismogram from Figure 7 displayed with the travel time curve tool in AmaSeis.  In this tool, the seismogram can be moved around on the screen until the selected P and S arrival times are aligned with the travel time curves.  The epicenter-to-station distance corresponding to the observed S-P time is then determined by the position of the seismogram and the specific distance, in this case 58.72 degrees, is displayed adjacent to the distance axis.

 

Using seismograms from three or more stations, the location of the epicenter can be estimated by triangulation.  For example, for the September 30, 1999 Oaxaca earthquake, seismograms for stations KIP, BINY, COLA and AMNO were displayed in the AmaSeis program, the P and S arrival time picked, and the epicenter to station distances inferred.  Using an inflatable globe, circular arcs are drawn on the globe corresponding to the epicenter-to-station distance for each seismograph station (Figure 9).  When all arcs have been drawn, the approximate epicenter location is determined by the intersections of the arcs (Figure 10).  Although this triangulation method is not the most reliable or accurate technique for locating earthquakes, it is relatively easy to understand and illustrates concepts of the travel times of seismic waves at increasing distances and earthquake location methods. 

 

Figure 9.  Using a piece of string marked at the appropriate distance in degrees (measure along the equator) and a felt pen (water soluble ink), a circular arc is drawn on an inflatable globe using the seismograph station (in this case, station AMNO) as the center of the circle.  Arcs are also drawn for other stations using the appropriate distances inferred from the S-P times.

Figure 10.  After all arcs have been drawn, the epicenter is inferred by the approximate intersection of the arcs.  Because of inaccuracies in the estimation of the S-P times and drawing the arcs on a globe, the intersections of the arcs may not be exactly a single point.  However, a reasonably  good  location is determined by this method.

 

Because the S wave arrival is not always prominent on a vertical component seismogram, the epicenter-to-station distance cannot always be inferred from AS-1 seismograms.  Furthermore, for seismograms from earthquakes that are located greater than 105 degrees from the station, no direct S wave arrivals are present due to the Earth’s core.  For earthquakes recorded at the West Lafayette, Indiana AS-1 station since April, 2000 (Table 1), distances inferred from the AS-1 seismograms are compared with the calculated distances (from the USGS reported epicenter to the station location) in Figure 11.  Although the distances generally correspond, the AS-1 distance determination appears to be accurate to only about +/- 4 degrees distance for distances greater than about 20 degrees.

 

More information on using the AmaSeis software is available at:

http://web.ics.purdue.edu/~braile/edumod/as1lessons/UsingAmaSeis/UsingAmaSeis.htm.  An S minus P earthquake location exercise is available at:

http://web.ics.purdue.edu/~braile/edumod/as1lessons/EQlocation/EQlocation.htm.

Figure 11.  Comparison of calculated distances (using station location and USGS epicenter location) with distance estimated from the S-P times on seismograms recorded by the AS-1 seismograph.  Distance estimates from the S-P times were determined using the travel time curve tool in AmaSeis.  Comparing actual and AS-1/AmaSeis S-P calculated distances.  N = 75; Standard Deviation = 2.51  degrees (November, 2004).

 

Ideas for Classroom Use:  Operating an AS-1 seismograph in a classroom or school building encourages awareness of earthquake activity around the world and provides an opportunity for teachers and students to work with real scientific data.  There is particular interest and excitement when a local or regional event occurs and is recorded by the seismograph or when a significant distant event happens.  Students will be interested in “checking the seismograph” each day and seeing how their records and magnitude estimates compare with the seismograms recorded at other stations and official magnitudes.  The occurrence of significant earthquakes around the world (there are about 20 events per year of magnitude of 7 or greater: many of these events cause significant damage) can be used to stimulate discussion, learning and research on geography, the causes of earthquakes, propagation of seismic waves, earthquake hazards, and earthquake safety.  Some specific suggestions for classroom use are:

 

1.      Maintain a catalog of seismograph recording.  Students can check the seismograph every day (or at regular intervals), perform routine maintenance (check that it is operating properly and perform a time check), identify possible recorded events and enter appropriate information into the catalog.  A hand written catalog is sufficient for recording such information as time corrections and approximate times of recorded events.  A more

 

complete catalog can be created using a spreadsheet (see Table 1, below) with information on earthquake to station distance and magnitudes.  Distance from the earthquake epicenter can be inferred from the P and S travel times as described above (AmaSeis provides a simple tool for performing this estimation; these times will not be able to be determined for all recorded events).  Magnitudes can be estimated using the procedures described in The AS-1 Seismograph – Magnitude Determination or using the online magnitude calculator at: http://web.ics.purdue.edu/~braile/edumod/MagCalc/MagCalc.htm.  A comparison between the AS-1 distance and magnitude information can be made by checking the USGS/NEIC, IRIS event search or IRIS seismic monitor sites on the Internet.  Instructions for accessing earthquake data on the Internet are included in

 http://web.ics.purdue.edu/~braile/edumod/eqdata/eqdata.htm.  All data should be written in the catalog to provide a record of activity of your seismograph station and document the comparison of distance and magnitude determinations.

 

Exercises that include magnitude calculations using AS-1 seismograms are available at:

http://web.ics.purdue.edu/~braile/edumod/as1lessons/EQlocation/EQlocation.htm and

http://web.ics.purdue.edu/~braile/edumod/as1lessons/magnitude/CalcMagnElect.htm.


 

Table 1.  Earthquake List -- Events recorded by AS-1 Seismograph, West Lafayette (40.44N, 86.90W) Indiana (L. Braile)

DATE

TIME(GMT)

LAT

LON

DEP.

USGS

USGS

USGS

USGS

AS-1

AS-1

AS-1

Calc. Dist

AS-1 Dist

Location

Comments

MM/DD/YY

HR:MN:SS

Deg.

Deg.

(km)

mb

MS

Mw

mbLg

mb

MS

mbLg

Deg.

Deg.

 

 

01/01/00

11:22:57

46.888

-78.930

18

4.7

 

 

5.2

 

 

5.2

8.610

 

Quebec

 

05/04/00

4:21:16

-1.110

123.570

26

6.7

7.5

7.6

 

 

7.0

 

132.060

 

Salawesi

 

05/12/00

18:43:18

-23.550

-66.450

225

6.2

 

7.2

 

6.5

 

 

66.480

65.3

Argentina

Int. depth, P,pP,PP,S

06/02/00

11:13:49

44.510

-130.080

10

5.8

5.7

6.2

 

5.8

5.5

 

31.830

32.9

Coast Oregon

Good S

06/04/00

16:28:26

-4.720

102.090

33

 

8.0

 

 

 

7.6

 

143.490

 

So. Sumatera

Long Surf wave train

06/21/00

0:51:47

63.980

-20.760

10

6.1

6.6

 

 

6.0

6.7

 

44.230

45.2

Iceland

 

07/11/00

1:32:29

57.370

-154.210

43

6.3

 

 

 

6.0

 

 

45.350

47.3

Kodiak Is., AK

 

08/04/00

21:13:03

48.790

142.250

10

6.3

7.1

 

 

6.1

7.1

 

81.080

81.6

Sakhalin Is.

 

08/06/00

7:27:13

28.860

139.560

394

6.3

 

7.3

 

6.3

 

 

98.660

 

Bonin Is. Region

 

08/07/00

14:33:56

-7.020

123.360

648

6.5

 

6.5

 

 

 

 

137.100

 

Banda Sea

 

08/09/00

11:41:48

18.200

-102.480

45

6.1

6.5

6.4

 

5.8

 

 

25.960

26.5

Michoacan, Mex.

Good S

08/22/00

20:12:14

36.490

-91.110

10

 

 

 

3.9

 

 

3.6

5.180

 

New Madrid reg.

 

08/28/00

15:05:48

-4.110

127.390

16

6.5

6.8

6.8

 

 

6.6

 

132.440

 

Banda Sea

 

08/28/00

19:29:32

-4.120

127.030

33

6.5

6.4

6.4

 

 

 

 

132.650

 

Banda Sea

 

09/28/00

23:23:43

-0.220

-80.580

22

5.8

6.0

6.6

 

5.6

5.6

 

40.920

 

Coast Equador

 

10/02/00

2:25:31

-7.980

30.710

34

6.1

6.7

6.5

 

 

6.6

 

116.050

 

Lk Tanganyika

 

10/04/00

14:37:44

11.120

-62.560

110

 

 

6.1

 

6.3

 

 

36.280

 

Windward Is.

 

10/04/00

16:58:44

-15.420

166.910

23

6.1

6.9

6.8

 

 

6.9

 

112.100

 

Vanuatu Is.

 

10/25/00

9:32:24

-6.550

105.630

38

6.3

6.6

6.8

 

 

 

 

144.400

 

Sunda Arc

 

11/01/00

4:27:46

-7.910

-74.470

151

5.9

 

5.9

 

5.8

 

 

49.490

 

Peru-Brazil Bor. Reg.

 

11/06/00

11:40:29

56.300

-153.350

33

5.5

5.6

6.0

 

5.6

5.6

 

45.040

 

Kodiak Is. Reg.

 

11/16/00

4:54:56

-3.960

152.270

33

6.0

8.2

8.0

 

 

7.8

 

115.760

 

New Ireland, PNG

 

11/16/00

7:42:17

-5.180

152.050

33

6.2

7.8

7.8

 

 

7.3

 

116.020

 

New Ireland, PNG

 

11/17/00

21:01:56

-5.450

151.680

33

6.2

8.0

7.8

 

 

7.6

 

117.200

 

New Ireland, PNG

 

12/06/00

17:11:07

39.620

54.770

30

6.7

7.5

7.0

 

6.5

7.2

 

92.940

 

Turkmenestan

 

12/07/00

14:08:49

37.930

-87.710

11

 

 

 

3.9

 

 

3.7

2.630

 

near Evansville, IN

 

01/10/01

16:02:42

57.090

-153.620

33

6.2

6.8

6.8

 

5.8

6.4

 

45.070

 

Kodiak Is. Reg.

 

01/13/01

13:08:41

40.740

-125.330

5

5.3

5.2

5.6

 

5.7

 

 

29.040

 

Off coast N. California

 

01/13/01

17:33:31

12.830

-88.790

39

6.7

7.8

7.6

 

6.5

7.5

 

27.550

27.6

Off coast C. America

 

01/16/01

13:25:00

-3.970

101.660

33

 

6.7

6.8

 

 

6.6

 

142.880

 

So. Sumatera

 

01/18/01

1:40:48

25.880

-110.380

10

5.0

 

 

 

5.0

 

 

24.370

23.4

Gulf of California

 

01/23/01

5:23:37

13.920

-90.990

120

5.7

 

 

 

5.4

 

 

26.710

 

El Salvador

 

01/26/01

3:03:19

41.990

-80.830

5

 

 

 

4.2

 

 

4.1

4.800

 

Ohio

Good S-P

01/26/01

3:16:41

23.400

70.320

24

7.1

7.9

7.7

 

 

7.8

 

112.990

 

So. India

 

02/13/01

14:22:08

13.650

-88.990

13

5.7

6.4

 

 

5.6

6.0

 

26.800

29.9

El Salvador

 

02/13/01

19:28:27

-5.080

102.440

36

6.7

7.2

 

 

 

7.1

 

143.710

 

So. Sumatera

 

02/17/01

20:11:28

54.250

-133.610

10

5.6

5.9

 

 

5.8

6.1

 

33.930

 

Queen Charlotte Islands

 

02/24/01

7:23:49

1.460

126.290

33

6.6

7.0

7.0

 

 

6.7

 

128.450

 

N. Molucca Sea

 

02/26/01

5:58:23

46.920

144.410

394

5.8

 

 

 

6.1

 

 

81.730

 

Sea of Okhotsk

 

02/28/01

18:54:33

47.150

-122.720

51

6.5

6.6

6.8

 

5.9

 

 

26.530

23.4

Nisqually (Seattle, WA)

 

03/15/01

13:02:42

-32.321

-71.492

37

6.1

5.6

6.0

 

?

?

 

73.820

 

Near co Central Chile

 

04/09/01

9:00:57

-32.668

-73.109

11

6.1

6.3

6.7

 

 

 

 

73.900

75.3

Off co Central Chile

 

04/14/01

2:20:13

56.080

-119.810

10

5.3

4.7

5.3

 

5.2

 

 

26.620

28.5

Alberta

 

04/19/01

21:43:42

-7.410

155.865

17

6.0

6.6

6.7

 

 

6.7

 

115.420

 

Solomon Islands

 

04/21/01

17:18:57

42.925

-111.395

0

5.4

4.9

5.3

 

5.6

 

 

18.450

18.2

Idaho

 

04/29/01

21:26:55

18.736

-104.545

10

5.2

5.5

6.1

 

5.2

 

 

26.460

 

Near co Jalisco, MX

 

05/04/01

6:42:13

35.205

-92.194

10

 

 

4.5

4.4

 

 

4.9

6.740

7.0

Arkansas

 

05/20/01

4:21:44

18.816

-104.446

33

5.5

6.0

6.3

 

5.5

6.3

 

26.350

30.9

Jalisco, Mexico

 

05/25/01

0:00:51

44.268

148.393

33

6.1

6.7

6.7

 

6.2

6.3

 

82.090

79.0

Kuriles

Dist from PP

05/25/01

5:06:11

-7.869

110.179

143

5.8

 

6.3

 

 

 

 

144.130

 

Jawa, Indonesia

 

06/03/01

2:41:57

-29.666

-178.633

178

6.8

 

7.1

 

 

 

 

109.770

107.0

Kermadec Is.

Dist from PP

06/14/00

19:48:48

51.160

-179.828

18

6.0

6.3

6.5

 

6.2

6.3

 

61.490

 

Andreanof Is., Aleutians

 

06/18/01

19:56:56

-24.291

-69.173

89

5.5

 

5.8

 

5.9

 

 

66.480

 

N. Chile

 

06/19/01

9:32:25

-22.739

-67.877

147

5.5

 

6.1

 

?

 

 

65.300

 

Chile-Bolivia border region

 

06/23/01

20:33:14

-16.265

-73.641

33

6.7

8.2

8.4

 

6.5

7.7

 

57.740

 

Near coast of Peru

Good complete seismogram

06/24/01

1:22:53

-17.585

-71.958

33

5.4

5.5

 

 

5.5

 

 

59.370

 

Near coast of Peru

 

06/26/01

4:18:31

-17.745

-71.649

24

6.2

?

6.8

 

6.2

 

 

59.600

64.1

Near coast of Peru

 

06/26/01

14:05:07

61.340

-140.070

10

5.8

 

5.8

 

6.0

 

 

38.130

42.6

S. Yukon territory

P,PP,S,SS

06/29/01

18:35:52

-19.522

-66.254

274

5.7

 

6.1

 

6.1

 

 

62.670

 

S. Bolivia

 

07/07/01

9:38:44

-17.543

-72.077

33

6.6

7.3

7.6

 

6.5

6.8

 

59.310

68.3

Near coast of Peru

 

07/19/01

18:00:40

57.203

-151.036

33

5.9

 

5.9

 

5.6

 

 

43.680

 

Kodiak Island area

 

07/24/01

5:00:09

-19.448

-69.255

33

5.7

6.2

6.3

 

5.9

 

 

61.800

 

N. Chile

 

07/26/01

0:21:37

39.059

24.244

10

6.0

6.6

7.0

 

6.1

6.4

 

78.980

 

Aegean Sea

 

07/28/01

7:32:43

59.025

-155.116

131

5.7

5.7

6.6

 

6.1

 

 

45.620

43.9

S. Alaska

 

08/02/01

23:41:06

56.260

163.790

14

5.9

6.2

6.3

 

5.7

6.2

 

66.720

 

Near E co Kamchatka

 

08/21/01

6:52:06

-36.813

-179.575

33

6.4

7.1

7.2

 

 

7.0

 

114.460

 

E of N Is. New Zealand

 

08/25/01

2:02:03

7.633

-82.766

25

5.9

5.7

6.1

 

5.9

 

 

32.870

33.6

S. of Panama

 

08/28/01

6:56:09

-21.722

-70.108

66

5.8

 

5.9

 

6.2

 

 

63.790

 

Near co of N Chile

 

09/04/01

12:45:53

37.143

-104.650

5

 

 

 

4.0

 

 

4.1

14.230

 

So. Colorado

 

09/05/01

10:52:08

37.143

-104.618

5

 

 

 

4.5

 

 

4.5

14.210

 

So. Colorado

 

09/07/01

2:45:59

-13.166

97.297

10

6.2

5.8

6.0

 

 

?

 

152.580

 

S. Indian Ocean

 

09/11/01

9:13:26

14.995

-91.571

161

5.0

 

5.7

 

 

 

 

25.680

 

Guatemala

 

09/14/01

4:45:12

48.904

-128.317

10

5.5

5.8

6.0

 

5.5

 

 

30.330

34.1

Off coast Vancouver Is.

 

09/16/01

23:20:09

48.540

-128.600

10

5.1

5.4

5.6

 

5.4

 

 

30.510

 

Off coast Vancouver Is.

 

10/12/01

5:02:34

52.850

-132.110

10

5.5

5.7

5.7

 

5.6

 

 

32.880

 

Queen Charlotte Islands

 

10/12/01

15:02:16

12.590

144.940

37

6.6

7.0

7.0

 

 

6.9

 

108.690

 

S. of Marianas Islands

 

10/14/01

1:10:45

-8.590

144.660

68

5.9

4.9

5.9

 

 

 

 

144.660

 

Jawa, Indonesia

 

10/17/01

11:29:09

19.313

-64.912

33

5.3

5.6

6.0

 

5.5

 

 

28.260

35.3

Virgin Islands

 

10/19/01

3:28:41

-4.043

123.933

10

6.3

7.3

7.5

 

 

6.8

 

134.350

 

Banda Sea

 

10/21/01

0:29:24

-36.992

179.030

33

 

6.8

 

 

 

6.7

 

115.500

 

Near E co N Is New Zeal

 

10/30/01

3:24:28

24.066

-109.038

10

5.3

4.9

5.5

 

5.4

 

 

24.740

 

Gulf of California

 

11/13/01

9:47:36

22.264

-106.949

33

5.5

5.8

6.1

 

5.5

 

 

24.830

 

Near co Cent Mexico

 

11/14/01

9:26:10

35.945

90.535

10

6.1

8.0

7.7

 

 

7.5

 

103.960

 

Qinghai Prov., China

 

11/28/01

14:32:32

15.560

-93.090

85

5.7

 

6.3

 

5.9

 

 

25.370

 

Near co Chiapas, Mexico

 

12/02/01

13:01:53

39.530

141.067

122

6.1

 

6.5

 

6.4

 

 

89.180

 

Honshu, Japan

 

12/12/01

14:02:35

-42.813

124.688

10

6.5

6.7

7.0

 

 

?

 

156.340

 

S of Australia

 

12/23/01

22:52:54

-9.613

159.530

16

6.2

7.0

6.7

 

 

6.9

 

114.090

 

Solomon Islands

 

01/02/02

17:22:48

-17.600

167.856

10

6.3

7.5

7.1

 

 

7.1

 

112.680

 

Vanuatu Islands

 

01/12/02

8:26:53

28.279

-69.566

10

5.7

4.9

5.4

 

5.7

 

 

18.720

19.0

Off E co United States

 

01/16/02

23:09:52

15.502

-93.133

80

5.8

 

6.4

 

5.8

 

 

25.430

 

Chiapas, Mexico

 

01/30/02

8:42:03

18.194

-95.908

108

5.6

 

5.9

 

5.7

 

 

23.490

30.3

Vera Cruz, MX, P,pP,S

 

02/14/02

23:23:13

14.975

-92.470

74

5.3

 

5.8

 

5.7

 

 

25.930

 

Chiapas, Mexico

 

02/22/02

19:32:42

32.375

-115.352

10

5.3

5.5

5.7

 

5.4

 

 

24.200

 

N. Baja

 

03/03/02

12:08:23

36.543

70.424

256

6.6

 

7.3

 

 

 

 

100.610

 

Hindu Kush, Afganistan

 

03/05/02

21:16:10

6.171

124.284

31

6.3

7.2

7.2

 

 

6.9

 

125.470

 

Mindanao, Philippines

 

03/27/02

11:18:04

30.138

-114.070

10

4.7

 

 

 

5.1

 

 

24.360

 

Gulf of California

 

03/28/02

4:56:21

-21.590

-68.170

122

6.2

 

6.5

 

6.4

 

 

64.130

 

Chile-Bolivia border region

P and pP phases

03/31/02

6:52:50

24.410

122.210

33

6.4

7.2

7.1

 

 

7.1

 

110.030

 

Taiwan

PP,SS, Good 20s surf waves

04/01/02

19:59:32

-29.490

-71.070

69

6.2

5.7

6.4

 

6.4

 

 

71.110

71.0

Near co. Central Chile

 

04/18/02

5:02:47

16.950

-100.820

33

5.3

6.0

6.3

 

5.6

 

 

26.300

28.9

Near co. Guerrero, MX

Good S-P

04/18/02

16:08:36

-27.350

-70.050

62

6.3

6.2

6.6

 

6.6

 

 

69.240

 

Near co. N. Chile

not shallow, weak surf. Waves

04/18/02

17:57:23

16.800

-101.020

33

4.9

 

4.9

 

5.4

 

 

26.540

30.3

Near co. Guerrero, MX

Also 4.9 event 3 min. later

04/20/02

10:50:45

44.510

-73.660

5

5.1

5.1

5.7

 

5.7

 

5.7

10.590

9.9

Plattsburgh, NY

Good S-P, Large Lg arrival

04/26/02

16:06:07

13.114

144.562

85

6.6

7.0

7.1

 

 

6.9

 

108.520

 

Near Guam, Mariana Is.

 

05/17/02

10:40:10

48.100

-27.829

10

5.6

5.4

5.7

 

5.6

 

 

42.060

48.0

No. Mid Atlanatic Ridge

PP-P

05/21/02

6:03:00

17.780

-81.916

10

5.3

5.0

5.7

 

5.5

 

 

22.990

 

N. of Honduras

 

05/25/02

5:36:31

53.930

-161.270

33

5.4

6.0

6.0

 

5.5

6.6

 

50.010

57.0

Aleutians

S-P

05/28/02

4:04:22

-28.890

-66.570

21

6.1

5.7

6.0

 

6.3

 

 

71.510

 

Argentina

 

06/05/02

12:45:16

35.347

-36.17

10

5.5

5.1

5.7 

 

5.5

 

 

39.890

 

N. Mid-Atlantic ridge

 

06/05/02

20:17:38

52.92

-74.42

18

 

 

 

4.5

5.2

 

4.2

15.060

 

N. Quebec

 

06/07/02

17:00:51

16.091

-96.637

33

5.5

5.0

5.6

 

5.8

 

 

25.740

 

Oaxaca, MX

 

06/13/02

1:27:18

-47.776

99.561

10

5.4

6.6

6.6

 

 

 

 

171.370

 

SE Indian Ridge

 

06/16/02

2:46:13

8.740

-84.026

33

5.4

6.2

6.4

 

5.6

 

 

31.710

 

Off Coast of Costa Rica

 

06/17/02

21:26:23

-12.581

166.349

33

6.0

6.6

6.7

 

 

6.5

 

110.780

 

Santa Cruz Islands Reg.

 

06/18/02

13:56:22

-30.754

-70.964

53

6.0

 

6.6

 

6.3

 

 

72.400

 

Chile-Argentina bor. Reg.

 

06/18/02

17:37:15

37.985

-87.778

5

 

 

4.4

5.0

 

 

5.3

2.590

2.8

near Evansville, IN

Right lateral strike slip

06/22/02

2:58:21

35.616

49.050

10

6.3

6.4

6.5

 

6.3

 

 

94.110

 

Western Iran

 

06/27/02

5:50:33

-6.990

103.790

10

6.1

6.9

6.6

 

 

6.8

 

145.310

 

SW of Sumatra, Indo.

 

06/28/02

17:19:30

43.770

130.720

564

6.8

 

7.3

 

7.2

 

 

89.540

 

E Russia -NE China Bor.

 

07/09/02

18:40:35

43.560

-127.227

10

5.6

5.5

6.0

 

5.7

 

 

29.930

31.7

Off coast of Oregon

 

07/31/02

0:16:45

7.929

-82.793

10

6.0

6.4

6.5

 

6.1

 

 

32.620

35.3

S. of Panama

 

08/14/02

13:57:56

14.190

146.130

65

6.1

 

6.4