TEACHING MOMENT: Using Seismology to Understand Wave Attenuation

TEACHING MOMENT: Seismology is one of the best tools to teach about wave theory, specifically wave attenuation.  Basic wave characteristics are shown below:

  1. A wave’s amplitude is how high the wave’s peak measures.
  2. A wave’s wave length is how long the wave measures from peak-to-peak.

Attenuation is to weaken the energy, force, magnitude, length or amplitude of an object.  After an earthquake occurs, the seismic waves travel throughout the Earth in many directions.  The closer earthquake instruments (seismographs) are to the earthquake’s location, the stronger the waves will appear.  A similar scenario is also true:  if several earthquakes occur and are recorded by the same seismograph, the earthquake closest and/or greater amplitude will appear the largest on the computer.

 

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TEACHING MOMENT

We keep watching the Earth shake every day, and the Earth is providing many “Real Life” teaching moments.  Today, 09/12/2018 at 06:29hrs UTC and at a depth of 110kms, a magnitude 5.3 earthquake shook Nicaragua.  Central America experiences earthquakes daily, some too small to feel!  Here in Spring, TX our station E1TX detected and recorded the event; however, our peers in Boston did not detect this quake.  We reviewed how far away the earthquake’s epicenter is from Spring, TX (20 polar degrees) and how far away Boston is from the epicenter (33 polar degrees).  Both cities are located close enough to the epicenter to “see” P,S waves – neither Spring nor Boston is more than 103 polar degrees away in the “Shadow Zone”….  why didn’t the seismograph in Boston detect the earthquake?

12092018_0629_scrnshtCOMPARE_NicaraguaPPT

 

 

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The Ring of Fire’s Last 24 Hours

It is remarkable observing how very active the Earth has been in just the last 24 hours (06092018 to 07092018).  Around the Ring of Fire, 4 moderate to major earthquakes have occurred.  A MAJOR M7.9 earthquake shook Fiji – the impressive focal depth was >650km deep inside the Earth!  Following seismic activity in Fiji, earthquakes occurred in Panama (M5.6), Ecuador (M6.2) and Chile (M5.8).  LOOK at the differences in amplitude between the events.  Which are smaller? larger? similar?  What other key piece of information would be useful when answering this question?

24 Hours of Global Shaking, September 6-7, 2018.

06092018_1549Fiji_07092018_0147_0212_0239_scrnsht_PanamaEcuadorChilePPT

 

 

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It Can Be Smaller in Texas, Too

Although Texas is known for it’s wide open spaces, big sky and large spacious prairies, it, too, experiences ground shaking from earthquakes.  A small magnitude 3.2 earthquake shook Timpson, Texas yesterday, September 4, 2018 at 15:06hrs UTC.  The focal depth was shallow at 5kms.  No damages have been reported.

East Texas, 09/04/2018 at 15:06 hrs UTC, M3.2

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3 Earthquakes and 1 (small) Tsunami

Over the past 24 hours, 3 moderate-to-major earthquakes and 1 tsunami occurred.  Station E1TX was able to detect 2 of 3 earthquakes, ironically the closest event was the one not recorded!  Shown below is a current screen capture from the EQ1 seismograph TXESP operates.

  1. A strong M6.4 earthquake in the Northern Mariana Islands at 08/28/2018, 22:35 hrs UTC and 60kms deep (detected)
  2. A small M4.4 earthquake in La Verne, CA  at 08/29/2018, 02:33 hrs UTC and 5kms deep.  This California earthquake may have a small magnitude, but it was lightly felt across most of Los Angeles (NOT detected)
  3. A MAJOR M7.1 earthquake in New Caledonia at 08/29/2018, 03:51hrs UTC and 27kms deep. (detected)This event **did** generate a very small 1 ft tsunami in the South Eastern Pacific Ocean.

New Mariana Islands, 08/28/2018 at 22:35 hrs UTC, M6.4

28082018_2235_29082018_0351_scrnht_NMarIslANDCalcedoniaPPT
24 hour summary of global Seismicity recorded at Station E1TX
29082018_2235_extract_NMarnIsl
Extracted seismogram of the M6.4 N. Mariana Islands earthquake.
28082018_2235_map_NMarIsl
Map of the epicenter of the N. Mariana Islands’ earthquake.

 

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The Ring of Fire is Active

A very deep (609kms) magnitude 7.1 earthquake shook Peru early this morning…. The M7.1 earthquake epicenter was near Iberia, Peru: the event began at 08/24/2018 09:04hrs UTC; because this earthquake occurred very deep, it’s likely that only light shaking was felt onshore.

Peru, 08/24/2018 at 09.04hrs UTC, M7.1

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Are we having too many earthquakes? Is the Ring of Fire too “hot”?  Not this year, despite the quite high seismicity in the past 7-10 days.  Courtesy of The Next California Earthquake (https://www.facebook.com/nextquake/) , here is one Table which explains the annual statistics of historical seismicity. “REMINDER: An average year has 12-17 magnitude 7+ earthquakes.  There have been 8 this year.” [as of today 08/24/2018 that number is now 9] ”

EQStatsTable2018

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The Powerful Earth Shakes Again

Its incredulous, but we have had two more powerful earthquakes in the last 24 hours.  A dangerous magnitude 7.3 earthquake shook Venezuela and several adjacent countries….TXESP watched LIVE as the teleseismic waves propagated across TX.  The M7.3 earthquake epicenter was near Yaguaraparo, Venezuela: the event began at 08/21/2018 21:31 hrs UTC and a deep focal depth of ~123.2kms. The second quake, a magnitude 6.2 event, occurred offshore Oregon hours later at 08/22/2018 09:31 hrs UTC and was 10kms deep; only light shaking was felt onshore.

TX-ESP and BC-ESP will have plenty of teaching materials given the elevated global seismicity in the past 7-10 days.

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21082018and2131_22082018and0931_scrnsht_VenezuelaAndOregonPPT

21082018_2131_map_Venezuela
Epicenter (star) of the M7.3 Venezuelan earthquake on 08/21/18 at 21:31 UTC
22082018_0931_map_Oregon
Epicenter (star) of the M6.2 Oregon earthquake on 08/22/18 at 09:31 UTC

 

 

The Powerful Earth

UNBELIEVABLE! **FIVE MAJOR** earthquakes in the past 24 hours. Shown below is the seismograms for: Colombia (M5.6), Fiji (M8.2), Indonesia (M6.3), Fiji (M6.8), Indonesia (M6.9)

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Note the similarities and discrepancies between the seismograms: which seismic wave phases were detected, the amplitude of these waves, and the duration (how much time) of each phase.

 

19082018_1701_LIVEscrnshtEQ1ppt

Energy of a M8.2 Earthquake Propagating Across the Earth

Today, an unbelievably powerful earthquake shook Fiji and the whole Earth….TXESP and Boston College watched LIVE as the teleseismic waves propagated across TX, VA and MA.  The M8.2 earthquake epicenter is near Ndoi Island, Fiji; the event began at 00:19hrs UTC with an extreme depth of ~563.4kms.

TXESP and Boston College, along with other academic colleagues, are learning from these recent large earthquakes to further classroom research efforts of the dynamic Earth.  We compare Raspberry Shake seismograms of teleseismic events and make observations about the similarities or discrepancies in the detection of multiple wave phases, their arrival times, and other details.

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Note the similarities and discrepancies between the seismograms: which seismic wave phases were detected, the amplitude of these waves, and the duration (how much time) of each phase.

19082018_0019_extractRScompare_FijiPPT

19082018_0019_map_Fiji
Epicenter of the magnitude 8.2 Fiji earthquake. Focal depth was >550kms.

**Seismograms courtesy of TXESP, J. Pulli and A. Kafka.

Magnitude 8.2 Shakes the Earth 360 deg

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Today, an unbelievably powerful earthquake shook Fiji and the whole Earth….TXESP and Boston College watched LIVE as the teleseismic waves propagated across TX, VA and MA.

The M8.2 earthquake epicenter is near Ndoi Island, Fiji; the event began at 00:19hrs UTC with an extreme depth of ~563.4kms.  At this time, no tsunami alert has been issued, although small tsunami waves were reported in local news media.  It’s not likely, thank goodness, that severe damage and injuries will be incurred due to the great depth of the focal point.

TXESP and Boston College, along with other academic colleagues, are learning from these recent large earthquake to further research efforts to understand the heterogeneity in the Earth.  We compare Raspberry Shake seismograms of teleseismic events and make observations about the similarities or discrepancies in the detection of multiple wave phases, their arrival times, and other details.

19082018_0019_LIVEscrnshtEQ1andRS_Fiji
Comparison of the magnitude 8.2 Fiji earthquake recorded on an EQ1 seismograph (top) and a Raspberry Shake seismometer (bottom).
19082018_0019_extract_Fiji
Extracted seismogram of the magnitude 8.2 Fiji earthquake recorded on an EQ1 seismograph.
19082018_0019_map_Fiji
Epicenter of the magnitude 8.2 Fiji earthquake. Focal depth was >550kms.

 

Watching the Earth Move From Costa Rica to Massachusetts

Today, shown is a comparison of three seismograms from a powerful #earthquake which shook Costa Rica….TXESP watched the #teleseismic waves #propagate across TX live.

The Mw6.0 earthquake epicenter is near Golfito, Costa Rica; the event began at 23:22hrs UTC with a depth of ~19kms. At this time, no tsunami alert has been issued. It’s too early for damage and injury reports, but TXESP will continue to monitor the section which is known for landslides.

Continuing with our research efforts to understand the heterogeneity in the Earth, we compare three Raspberry Shake seismograms of this event.  Note the change in amplitude and wave phases as the teleseismic waves move from Costa Rica, through TX and VA, and finally to MA.  What do you observe?

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**Seismograms graciously provided by TXESP, J. Pulli, and A. Kafka

17082018_2322_extractRScompare_CostaRicaPPT

 

 

Comparing Seismograms of M6.5 Earthquake in Indonesia

Shown is an image comparing a powerful #earthquake which shook Indonesia at 15:35 hrs UTC, the focal depth was a deep ~539kms.  The figure below demonstrates how the #teleseismic waves #propagated across Spring TX, Oakton VA and Boston MA.  How could you explain the differences in first wave phase arrival times and amplitudes?

The M6.5 earthquake epicenter is near Kampungbajo, Indonesia.  At this time, no tsunami alert has been issued.  It’s too early for damage and injury reports.

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17082018_0535_extractRScompare_Indo

17082018_1535_map_Indo