Thursday, December 31, 2020

Exploring diffusion for hillslope changes using a spreadsheet

I became obsessed with diffusion erosion modeling in my PhD work. It is a simple (certainly oversimplified) way to think about how hillslopes may change over time in the absence of mass wasting, debris flow, and fluvial processes. There is a lot to say about it, but I wanted to capture a few items I recently developed.

Here is an explanation and assignment on the topic in my Computers in Geology class: Lecture 8: Exploring diffusion using Excel.

One of the challenges that I have had in some applications is that the computational "space" was too small in the spreadsheet, given that it is fixed. Of course this is not a problem if one dynamically determines the number of time steps for example based on a stability criterion and you do it with a for or while loop in something like Matlab. So, when I was helping Emily Apel with her senior thesis recently, I built her a big spreadsheet (seemed easier given the limited time that she had.

Here is the original spreadsheet with only 27 space steps and 191 time steps. It is good for teaching and quick demos: LINK to Spreadsheet.

Above is the screen cap of the main interface page where the user just changes the bold cells and watches the calculations in real time.
Above is the screen cap of the Model Calculation Space tab which shows the compuational engine with its fixed elevation boundary conditions and explicit centered in space and forward in time finite differences.

Here is the big spreadsheet with 250 space steps and 1000 time steps: LINK.

And, here is a video that I built to explain the general activity for Emily Apel, but it may be useful for others. It explains the two spreadsheets that are linked above.

One of the cirtical concepts that is accessible in both of these spreadsheets is the opportunity explore not only initial step models, but also continuously displaced scenarios.

Here are a few other blog posts and recent publications which might be of interest as well:

Tuesday, December 15, 2020

Simple computations of scalar seismic moment and moment magnitude

In my classes and for research, sometimes it is useful to calculate the scalar seismic moment (M0; basically a geometric measure of the total static energy release at a 0th order). It is a function of the area of a fault that slipped times the average slip times the shear modulus of the volume. The latter is usually assumed to be 30GPa. The main challenge (after determining the parameters) is to get the units all to be the same (dimensions of Newtons and meters):

M0= mu*Length*Width*U_bar.

And, once we have that scalar moment in Nm, then we usually want to convert it to moment magnitude (Mw):

Mw = 2/3 log10(M0) – 6.

Here is a simple spreadsheet to do this calculation: LINK
Here is a simple and older lecture I have used in introductory level geoscience courses: LINK

Sunday, December 13, 2020

New fast workstation and sUAS capability for School of Earth and Space Exploration course development


Our geoscience courses have benefited from plenty of course development, especially lately as we have moved online and virtual. I recently was able to invest SESE course fees to build out our capabilities for high resolution mapping and 3D work. Javier Colunga built a nice and fast Windows workstation, and we also purchased a Mavic Pro 2 sUAS system. The descriptions are below for reference.

Workstation description

We have been building these "gaming" style fast desktops for a while and this latest incarnation is powerful for graphics intensive and 3D work, especially structure from motion photogrammetry (e.g., Johnson, et al., 2014 and GSA short course).
Here is a short description of the hardware (cost approx. $5k):

  • CPU: Ryzen Threadripper 3970X 32-core/64-thread (with a premium cpu cooling solution)
  • Main Memory: 128GB DDR4 3600
  • Graphics Card: GeForce RTX 2080 Super
  • Storage: Samsung 1TB M.2 NVME OS drive, additional 4TB hard drive
  • Operating system: windows 10 Enterprise
  • Input: Logitech wireless keyboard and mouse
  • Monitor: HP 27 inch 1440P
Here is the main software installed:
  • Google Earth Pro
  • Matlab R2020a
  • Camtasia 2020
  • Cloudcompare
  • Agisoft Metashape
  • ArcGIS 10.7
  • QGIS
Here is more description, how to connect remotely, and a sign up sheet. LINK

sUAS description

For SESE, we have purchased a DJI Mavic 2 Pro (actually the FlyMore combo so it has a nice case and 3 batteries). This is a nice mapping and aerial documentation system.

Devin Keating has been helping to get the system into production mode. He has built a nice documentation of the system and its use. He also registered it with the FAA so we have a tail number. See this LINK. To operate it, one should have the part 107 Remote Pilot certification. And, there are ASU oversight requirements as well.

Recent course related work using this type of system (and computed on the nice workstation described above):

Warford Ranch volcano (Arizona) sUAS mapping

Virtual field geology exercises for GLG451 Field Geology I Spring 2020

Material for virtual exercises for GLG452 Field Geology II at Camp Tontozona AZ