I introduced the ideas behind human triggered seismicity.

Sarah Minson visited class virtually and presented some important, interesting, and subtle aspects of “earthquake” early warning system performance and possibilities.

I reviewed the history of earthquake catastrophes and the patterns in earthquake fatalities over the last few hundred years.

Students completed an in-class activity on forecasting the number of earthquakes into the future. The exercise is available on Canvas.

Today, students completed on in-class exercises. “Can you outrun a tsunami” using video frame from the 2011 Tohoku Earthquake tsunami.

While working, students watched the video linked below, which documents the arrival of the 2011 Tohoku  Tsunami in Kesennuma City, Japan. Kesennuma is in the Miyagi Prefecture of northern Japan. As of September 2015, the city population was 65,434 (google). The city is near the northern end of the 2011 rupture, and like much of the region, was hit by a strong tsunami following the event.

East coast of Honshu Japan (from Google Maps) showing the location of major cities, including Kesennuma (to the north). Source: Google.

Zoom into the Kesennuma Region, showing the location of the bay and rivers. The video was shot along the small O River meandering from the upper right down into the bay. Source: Google.

I introduced the topic of tsunami and described how tsunami and large earthquakes are related to subduction. No in-class activity.

I presented a lecture on the origin of the Universe, including the Big Bang and the origin of elements. I had three objectives: To outline scientific hypotheses for the origins of the Universe and of Earth. I introduced

• The basic structure of the Universe
• The immensity of the Universe
• The depth of Time

This is a very broad view of Earth’s origin, but these are some of the most fundamental contributions of science to human thought – I encourage you to explore them more on your own, when you have time.

The slides are on Canvas, and we did not complete an in-class exercise.

Students completed an in-class exercise using information on plate motions, and aftershocks to investigate some characteristics of the Mw 7.9 20015 Gorkha Nepal earthquake.

See the Canvas assignment for details if you missed the class. Note that I just now updated the worksheet on Canvas to match what students did in class.

Students completed two in-class exercises

Temporal Aftershock Patterns

Seismic Moment, Rupture Area, and Fault Slip

That’s all – no lecture, no slides.

We continued our discussion of earthquake patterns (seismicity patterns) focusing today on temporal patterns, including the last century of large earthquake history. We also discussed foreshocks, mainshock, and aftershocks.

Omori’s “Law” describes the typical temporal evolution of an aftershock sequence, $$n(t)=\frac{K}{(c+t)^P}$$ which is the equation of a hyperbolic decrease in the number of aftershocks following an earthquake. The values of \(K\),  \(c\), and  \(P\) vary from earthquake sequence to sequence, but are generally constant for any particular sequence.  \(t\) represents time.

What does hyperbolic mean? The number of aftershocks in a fixed time interval (think day) decreases very fast early in the sequence, but then decays slowly much later. Typically,  \(P\approx 1\) so the number of aftershocks decreases as the inverse of time. Not all sequences follow this form, but even then, Omori’s Law is a good reference to use to compare and contrast earthquake-sequence temporal histories.

Another pattern is Båth’s “Law”, a rule-of-thumb that indicates that the largest aftershock is roughly about one magnitude unit smaller than the mainshock.

Students completed an in-class exercise related to elastic rebound, looking at the strain accumulation occurring near the central San Andreas Fault. The data we used are from

Schmalzle, G., Dixon, T., Malservisi, R., & Govers, R. (2006). Strain accumulation across the Carrizo segment of the San Andreas Fault, California: Impact of laterally varying crustal properties. Journal of Geophysical Research: Solid Earth, 111(B5).

You can see the worksheet on Canvas.

We continued talking about the definition of an earthquake.  The common definition is, of course, the shaking of the ground. We use the term to refer to the source of the ground shaking:

• An earthquake is a sudden release of energy caused by sudden motion (slip) along a fault.
• The energy is stored in the rocks adjacent to the fault and accumulates slowly (over 10’s to 1000’s of years) but is released quickly (in seconds or minutes).
• The suddenness of energy release generates seismic waves that shake the ground as they travel outward from the earthquake “source” region.

Key features of an earthquake rupture.

Sliding during an earthquake begins at a location called the hypocenter. As the rocks slide, their friction decreases, which makes it easier to slide. Sliding in one region induces motions in the adjacent regions (those that are strained) and the area that is moving grows rapidly. Most of the slip occurs quickly. Eventually the rupture encounters a region of low strain (perhaps because of an earlier earthquake) or a region unready to fail and the rupture ceases.

Students completed their first blog posts (https://sites.psu.edu/eqsocarchive/).

We began with a couple of back-of-the-envelope calculations. First we estaimted the number of air molecules in our classroom (\[\approx 10^{28}\]). Then students worked on an in-class activity relating heat flow out of Earth with energy input from the Sun and energy consumption on campus and across the United States.

To provide an intuitive feeling for what happens in earthquakes I showed some example videos recorded during earthquakes. Most of the examples showed moderate levels of shaking, but a few showed how violent the shaking can become in large earthquakes. The clips are from YouTube.

The goal is to watch the videos and look for patterns in shaking – observe what happens near small and large earthquake.

California KTLA Anchors:

Alaska, 2018

California Judge Judy:

Van, Turkey Earthquake:

Coast Rica, 2012:

California 1989:

Japan Kobe:

Ridgecrest, CA (2019)https://youtu.be/dgamBCvgDAw

Tohoku, 2011

I talked about the Tonga volcanic eruption and tsunami and then reviewed a little bit of mathematics:

• Exponents
• Scientific Notation
• Logarithms 
• Rough Estimation

Hand outs:

• Copies of the slides
• Assigned reading: What is an earthquake? (quiz online, due Monday evening)

Assigned homework: Describing global earthquake spatial patterns (due Monday before class).

Students completed an in-class activity “Observing and Doing”

Given that mathematics is “the study of abstract patterns and relationships”, it is obviously a natural tool for scientific study, which is focused on patterns.

Required Readings:
The readings are available on Canvas. They cover much of the same material from a historical, practical, and summary perspective.

• Chapter on Logarithms by Stewart
• Excerpt from Guesstimation by Weinstein
• Exponents and logarithms (Schaum’s Outline summary)

Optional Reading: Judge Jones’ ruling in the Dover Science Education Case (2005)

Useful handouts:

Online quiz: Science & Mathematics Quiz (Due 19 January)