BIG HEAD “My biggest fault is that the faults I was born with grow bigger each year." - Haruki Murakami

Precariously Balanced Rocks (PBR)

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Do you like hiking? Have you wandered around the beautiful landscape of Utah and seen the amazing precariously balanced rocks scattered around? Have you ever wondered why they exist, especially with so many large earthquake-generating faults around? You can help me do science!

Because of their fragility, PBRs act as reverse seismometers; they tell us which earthquakes haven't happened. I map out the locations of these PBRs all over Utah, especially near the Wasatch fault zone, and I make 3D models of them with my students. We then shake these models in a computer earthquake simulation to measure the force required to knock the PBR over. Because the PBR is still there, we know this earthquake has never happened; this provides a limit on the largest earthquakes that could've happened in the past and what their shaking patterns might look like.

If you want to help, simply take a picture of any Utah (or anywhere, really) PBR you happen to find while out hiking/rafting/climbing/etc. and email it to me! Just send me:
A photo
Latitude & Longitude
A short description of where you found the PBR
Make up a cool name for the rock!

You can reach me at: amir.allam@utah.edu

Thanks for your help!

An earthquake simulation of Echo with 0.25g maximum horizontal acceleration. The PBR gets knocked over, thus an earthquake this strong never happened.
An earthquake simulation of Echo with 0.20g maximum horizontal acceleration. This earthquake is too weak to knock the PBR over, so it could have happened.

PBR Locations

Echo

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The Georgian

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The Witches

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Hand of God

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Compound

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Slickback

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