Untold stories of rocks, after parties and the San Andreas Fault | Amy Moser | TEDxUSU

Translator: Jeff Broadbent
Reviewer: Denise RQ This is a rock. It’s from Southern California,
but not originally. It’s been through some rough times
in it’s life; an earthquake or two. And not to mention how often it’s dealt
with the other dynamic processes going on within the Earth. You see, this isn’t
just any ordinary rock. Just like human beings,
every rock has a story; a unique history that brought it from the depths of the Earth
to the surface, and the details hidden
within rocks are critical for understanding everything from earthquakes
to mountain ranges and geologic time. As a geologist, I’ve interacted
with a number of amazing rocks in my day, but the story of this one right here
is definitely not like the rest. Let me tell you a tale
of this rock’s intricate journey, and how that journey
crossed paths with my own, resulting in several life
and rock-changing moments along the way. So this rock’s story begins
some 65 million years ago when it formed, sitting very, very deep within the Earth
at extreme temperature and pressure. That’s right. When T. rex and Allosaurus
are getting squashed by a meteor on the Yucatan peninsula, suffocating from the fumes
of unprecedented volcanic eruptions, our friend here is none the wiser, but still undergoing a number
of important changes of its own. We know this because rocks record
their story internally; sort of like how you might keep
a record of your life in a journal, so too does a rock record its story
in its textures and compositions. Some minerals even record when specific chapters
in a rock’s story happened, like adding a date to your journal entry. As geologists, we can date these minerals,
flipping back through the pages to find out when certain parts
of a story were written. By 25 million years ago, this rock begins
its journey to the surface of the Earth, cooling to about 150 degrees Celsius, and sitting five to six kilometers
beneath the Earth’s surface. The Earth has an internal heat source, and as rocks move from the deepest parts
of the Earth closer to the surface, they cool from incredibly hot temperatures to the temperature of this room
we’re sitting in right now. So, for the first 52
to 59 million years of its life, this rock dealt with
some major rock-changing events. But nothing, absolutely nothing compares to when the big one makes
its grand entrance. Between six and twelve million years ago, the San Andreas Fault, arguably,
the most famous fault in the world, starts to shake things up. When the two sides of a fault
move past one another very rapidly, that’s an earthquake; and when earthquakes happen,
the rocks surrounding the fault become incredibly fractured,
busted up, and damaged. In geology, we call this fracturing
and busting up deformation, and the deformation,
or deformed area around the fault, is the fault damage zone. The fault damage zone is perhaps
one of the richest records available to a geologist. Every little small fault, fracture,
and mineral in the fault damage zone is tied to the story of the fault. Think about it like an afterparty. After the main event – so the Oscars, a movie premiere,
or in this case, an earthquake – all of the excitement, food, music,
and dancing is moved elsewhere – into the fault damage zone – so that the celebration can continue. Think about what you can learn about
what really went down at the main event by talking with everyone who made it
all the way to the afterparty. In the same way,
studying fault damage zones is the ideal window through which to see
the story of a fault through time. Finally, after the appearance
of the San Andreas Fault, after this rock gets incorporated
into the San Andreas Fault damage zone, it makes its final ascent
to the surface of the Earth. And that is where our understanding
of this rock’s story sat, until I came along,
and everything changed. When I visited Utah State University
as a potential graduate student, my now adviser
and several other professors took me to take a closer look
at one of their key field research areas. Just east of Willard, Utah, where the Wasatch Mountains
begin to rise out of the Great Salt Lake, the damage zone of a slightly less famous, but still incredibly important,
Wasatch Fault is exposed. The Wasatch Fault damage zone
has a number of small faults coated in a metallic,
reddish-purple mineral called hematite, and in some places, these fault surfaces
are so smooth and reflective you can actually see your face in them. These were easily
some of the most beautiful rocks I had ever seen. And trust me, I’ve seen a lot
of really cool rocks. (Laughter) So imagine my reaction when I learned
there were rocks very similar to those in the Wasatch Fault damage zone
that existed in Southern California, tied to the San Andreas Fault
of all things, and that I could work on if I decided to come
to Utah State for graduate school. How in the world could I say no? I cite this as the moment that ultimately led me to this rock
and my research on the San Andreas Fault. While based on what I’ve already told you, it may seem like we know
everything there is to know about this rock’s story, in reality, there are some crucial gaps
regarding the San Andreas that we know very little about. We have a good idea of
when the San Andreas developed in general, but when was deformation,
that fracturing and busting up occurring in the part of the San Andreas
Fault damage zone that this rock is from? Ultimately, we need to know
when did the afterparty start? How long did the afterparty last? And what in the world
was going on at this afterparty? These are important questions because faulting and deformation
are not simple occurrences, especially in Southern California. This is an afterparty with dancing,
music, games, and ten kinds of dip that may even get broken up by the cops
and reconvene multiple times throughout the evening. (Laughter) Acquiring additional details
of this rock’s story will therefore help us understand
how the fault operates and predict how it might behave
in the future. That’s why we turn
to the fault damage zone, our afterparty record,
to see what we can learn. So, if we need to know about time, wouldn’t it be nice if there were
something, anything, like a mineral that we could date in order to answer
our outstanding questions about this rock’s story? I didn’t just pick up this rock
from the San Andreas Fault damage zone because it looks cool. Just like the Wasatch rocks,
this rock has a very small fault coated in metallic,
reddish-purple mineral – hematite. Not only can we date hematite but this hematite is tied to the story
of the San Andreas Fault. Dating it, therefore, might provide
valuable insight into this rock’s story. Despite all of the possible complications
that accompany dating hematite, especially in faults, the hematite from
the San Andreas Fault damage zone told us exactly what we hoped it would. During the period between 300,000
to 700,000 years ago, right in the middle of woolly mammoths, saber-toothed tigers,
and our early hominid ancestors, this damage zone was deforming
– possibly via earthquakes – and the hematite formed
in the damage zone as a result. We have effectively documented
a 400,000-year-long period of earthquake after earthquake
after earthquake, with a reconvening afterparty
following each main event. I don’t think I can even begin to impress
how ridiculously amazing these new details
of this rock’s story are. Hopefully, just me standing up here
being incredibly stoked and exasperatedly trying to explain it
to you will do the trick. But in a more concrete sense,
we now have a better understanding of the complicated history
for this section of the San Andreas. There’s been a lot going on at
this afterparty in the last million years. It’s just so incredibly difficult to say
when deformation was occurring, and to do something like that
for the San Andreas Fault? That’s a really big deal. In so many ways, this isn’t
just a big deal for science, but it’s also a big deal
for me personally. I am, at my core, a geologist,
and plan to be for the rest of my life. My research is
a fundamental part of who I am. It defines me as a scientist, but more importantly,
it defines me as a human being. One thing I often think about is how every time I pick up a rock
and add it to my research sample suite, I am inevitably changing
the very story I’m trying so hard to tell; both the rock’s and my own. But in doing so, I have become
an important component of this rock’s story. If not for me and my research, this rock may have sat at the surface
of the Earth for a very long time, waiting for the next indeterminate step
in its adventure, its story untold. Instead, it also sits up
on this stage today, not only a new piece
in our understanding of the San Andreas but also the cornerstone
of my own geologic story. Ultimately, this rock took a journey,
and I took a journey. Once the two intersected,
neither were really ever the same again. (Applause)


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