WEBVTT Kind: captions Language: en 00:00:10.240 --> 00:00:14.700 Ever wondered how to read the data on a seismogram? 00:00:14.700 --> 00:00:21.300 The webicorder is the digital version of the paper records used by scientists in days of 00:00:21.300 --> 00:00:22.680 yore. 00:00:22.680 --> 00:00:25.700 Seismometers measure vibrations. 00:00:25.700 --> 00:00:28.550 More vibration… more wiggle. 00:00:28.550 --> 00:00:32.000 Some seismometers measure only up and down. 00:00:32.000 --> 00:00:36.800 Sometimes, they shake too much and data are off-scale. 00:00:36.800 --> 00:00:41.000 Some seismometers record in all three dimensions. 00:00:41.000 --> 00:00:47.489 Many webicorders display 15 minutes per line, alternating colors as time passes. 00:00:47.489 --> 00:00:52.030 Plots are automatically updated every few minutes. 00:00:52.030 --> 00:00:57.089 Scientists use webicorders for a quick look at current activity, but webicorders are really 00:00:57.089 --> 00:01:03.019 just a blurry picture of the actual data To really understand what’s going on, they 00:01:03.019 --> 00:01:06.180 look at the real data, which is far more informative. 00:01:06.180 --> 00:01:08.750 Here is a small earthquake. 00:01:08.750 --> 00:01:16.100 It begins as a sharp crack as the rock breaks, and then quickly decays with time. 00:01:16.100 --> 00:01:20.610 In this plot, the data are clipped to allow viewing of other data. 00:01:20.610 --> 00:01:26.109 That can be very useful when there are lots of earthquakes, as in this seismic swarm, 00:01:26.109 --> 00:01:31.119 with multiple earthquakes of magnitude 2 to 3. 00:01:31.119 --> 00:01:35.039 Seismometers are sensitive enough to pick up vibrations from earthquakes around the 00:01:35.039 --> 00:01:37.749 world – if they’re big. 00:01:37.749 --> 00:01:45.869 This is what the giant 2011 Japan earthquake looked like on a seismometer in Wyoming, 5000 00:01:45.869 --> 00:01:47.329 miles away. 00:01:47.329 --> 00:01:53.549 Compared to the P and S waves that travel through the earth, surface waves are slower 00:01:53.549 --> 00:02:00.319 and arrive later, but can continue to be recorded for hours as they propagate around the earth. 00:02:00.319 --> 00:02:07.220 Seismometers record not only earthquakes but anything that can make the ground vibrate: 00:02:07.220 --> 00:02:18.580 Helicopters, Ocean waves, Traffic, Animals and Wind. 00:02:18.580 --> 00:02:20.780 Wind can be seen as noisy periods. 00:02:20.780 --> 00:02:25.840 Here, the wind picks up each day and drops off at night. 00:02:25.840 --> 00:02:34.500 Here, traffic noise shows up on a seismic station located a quarter mile from a road. 00:02:34.500 --> 00:02:41.920 Seismometers are sensitive electronic instruments often deployed in harsh wilderness environment. 00:02:41.920 --> 00:02:46.400 They can and do break. 00:02:46.400 --> 00:02:53.220 Sometimes they just stop working, but sometimes they just become noisy and unreliable. 00:02:53.220 --> 00:03:01.070 Here’s a record from a three channel instrument, one of which is broken – guess which one? 00:03:01.070 --> 00:03:05.960 Nearby equipment and machinery can also create interference. 00:03:05.960 --> 00:03:08.290 Worried about something on a webicorder? 00:03:08.290 --> 00:03:12.010 Then check readings from nearby instruments. 00:03:12.010 --> 00:03:18.480 Anything that shows up on only a single seismometer is either noise or earthquake activity too 00:03:18.480 --> 00:03:20.650 small to worry about. 00:03:20.650 --> 00:03:21.650 OK. 00:03:21.650 --> 00:03:27.410 You’ve done your homework and you’re ready to graduate from the “Acme School of Webicorder 00:03:27.410 --> 00:03:28.840 Arts and Sciences.” 00:03:28.840 --> 00:03:29.840 Congratulations. 00:03:29.840 --> 00:03:33.930 You’re now prepared to start cruising data on the internet. 00:03:33.930 --> 00:03:39.910 Have fun out there, mind your s’s and p’s, and please keep in mind, if you see an ominous 00:03:39.910 --> 00:03:46.960 signal at Mount Scarrymore, don’t hesitate to seek the opinion of a professional seismologist. 00:03:46.960 --> 00:03:50.890 They have many years of training, and on-the-job experience. 00:03:50.890 --> 00:04:21.910 And they all have their favorite story for that funny signal no one can explain.