WEBVTT 00:00:06.000 --> 00:00:14.000 Hi, my name is Andrew Dunning and I'm recording my presentation for the 2021 Student Research Symposium. 00:00:14.000 --> 00:00:29.000 My research topic, I'm a graduate student here at Portland State University in the geology department, and my research topic is primarily concerned with the age of an earthquake in Eastern Oregon finding out when the last time in earthquake happened on 00:00:29.000 --> 00:00:33.000 this recently discovered fall. 00:00:33.000 --> 00:00:40.000 So allow me to get my presentation, started here and I will begin. 00:00:40.000 --> 00:00:52.000 Alright so the title of this presentation is evaluating active faults and earthquakes in a strawberry mountains in Oregon. 00:00:52.000 --> 00:01:05.000 So a little bit of background here to possibly active faults were discovered by state geologists in Maidan, who was with the Department of geology and minerals industries in the strawberry mountains, which are here. 00:01:05.000 --> 00:01:07.000 Far Eastern Oregon just south of the city of john day. 00:01:07.000 --> 00:01:24.000 the city of john de, and the way they were discovered was using a method of mapping the topography called LIDAR, which is short for an acronym for light distance and ranging, and this maps the ground surface using lasers from aircraft as my study area 00:01:24.000 --> 00:01:31.000 is marked here in yellow it's about, about a six hour drive from Portland and it is a stunningly beautiful part of the state. 00:01:31.000 --> 00:01:41.000 So when we look at my map here I have mapped the fault scopes, using information provided by in Maiden, and these have been slightly enhanced PowerPoint. 00:01:41.000 --> 00:01:57.000 So we have two main fault zones here in the strawberry mountains. One trending east to west here and another further south trending north to south. This is called sheep mountain, and this has been in other literature been called the john de fault. 00:01:57.000 --> 00:02:03.000 But until recently no activity was known on this call it was thought to be not active. 00:02:03.000 --> 00:02:18.000 So there are about 7000 people living in the john de Valley This is Grant County, which is a rural remote county and the area has one of the lowest earthquake hazard ratings in the West, as per the national seismic hazard maps and active faults in this 00:02:18.000 --> 00:02:33.000 area would both increase the seismic hazard that is known for the people of the john de Valley, but it would also shuffle what we know about tectonic province tectonic processes in this part of the Northwest. 00:02:33.000 --> 00:02:38.000 So to sort of dive headfirst into the geology here. 00:02:38.000 --> 00:02:43.000 It's both simple and complex. 00:02:43.000 --> 00:02:57.000 So I've color coded the rocks here based on age, and we see a lot of this sort of green color, these are all rocks that are Miocene and age, which is from between 5 million, and I believe about 20 million years old. 00:02:57.000 --> 00:03:05.000 A lot of them are, in fact, similar and composition there and decide and the Celtic lovers, but mixed in with a few other rock types in there as well. 00:03:05.000 --> 00:03:12.000 The oldest rocks in the area are this blue color, they go back to the Permian which has over 400 million years ago. 00:03:12.000 --> 00:03:31.000 And this blob a very old rock is very interesting in that it is bounded by the john de fault on one side, but not on the other. 00:03:31.000 --> 00:03:38.000 And as a result of that this fault zone coincides roughly 50% of the time, with previously mapped a bedrock faults. 00:03:38.000 --> 00:03:46.000 And these are ancient faults that have been offsetting rocks, a long time ago and we're not again not thought to be active until very recently. 00:03:46.000 --> 00:04:00.000 Here you can see this older sort of pinkish orange colored rock has been offset adjacent to younger green colored lava rock sees it both lava rocks, effectively. 00:04:00.000 --> 00:04:16.000 And so for the plate tectonics that are affecting this region driving earthquakes. We have to zoom out a bit you can see here the Northwest. This is a model created by wells and Simpson, to sort of interpret the crystal rotation of the Pacific Northwest 00:04:16.000 --> 00:04:23.000 we have measured from GPS units that the entire Northwest is rotating in this clockwise direction. 00:04:23.000 --> 00:04:41.000 And that's because the Sierra Nevada and related fault systems to the south, are pushing the Sierra Nevada Mountains block into the Oregon Coast Range and Klamath mountains, which are located here, which causes Oregon to swing out and polls on, Nevada, 00:04:41.000 --> 00:04:46.000 and South Eastern Oregon here creating what we call the basin and range province. 00:04:46.000 --> 00:05:02.000 So the Blue Mountains which are here in my study area again is in red, sort of occupy a transitional zone between extending basin and range, and stable North America, which is up here. 00:05:02.000 --> 00:05:17.000 of complicated ways. So previously. Other models have assigned to the brothers fault zone which is here and read to be the northern limit of this base and range extension, but finding out that this fall appear the john default is active would shuffle 00:05:17.000 --> 00:05:21.000 that timing a little bit. 00:05:21.000 --> 00:05:28.000 So I'm going to zoom in a bit here to analyze fault surface expression in other words how do we know that there's an active fault here in the mountains. 00:05:28.000 --> 00:05:33.000 So I'm going to zoom into this area in the map here. 00:05:33.000 --> 00:05:49.000 So during an earthquake fault moves the valley side of the fault drops down in the mountains uplift and this creates what's called a startup, and a scarf, this scarf that I've mapped here and read offsets glacial deposits and volcanic rocks, both of which 00:05:49.000 --> 00:05:57.000 we can take to the lab and date using a variety of methods or find what we call an absolute age. 00:05:57.000 --> 00:06:03.000 So I'm going to zoom into a site right here this is on strawberry Creek. 00:06:03.000 --> 00:06:17.000 So here you can see the fault scarf, it creates sort of the scar across the landscape. I've marked in here at these blue arrows and I want to just to make it clear that it is visible from the air and this is again that LIDAR map. 00:06:17.000 --> 00:06:29.000 So the lasers are sort of bounced from the aircraft they bounce off the ground and are detected, and we are able to use that to create this map, And this displaces. 00:06:29.000 --> 00:06:42.000 This right here which is a glacial morning which is deposited by a large glacier. There aren't any glaciers now but these days, likely from the last Glacial Maximum which is what geologists called the most recent ice age and across this fault system, 00:06:42.000 --> 00:06:50.000 we see generally one to two meters of vertical offsets that would have happened over the course of the earthquake perhaps on the order of a minute to two minutes. 00:06:50.000 --> 00:07:05.000 And we have about one and a half meters of offset here at strawberry Creek, which looks like this and you can see how the slope here, marked by these green lines has been offset, one and a half meters here across the default here. 00:07:05.000 --> 00:07:18.000 So we, that gives us a question that was when was the last time an earthquake occurred on this fall, because that gives us an idea of how likely it is to generate an earthquake in the near future and therefore does it pose a hazard to the people in the 00:07:18.000 --> 00:07:20.000 in the john de Valley. 00:07:20.000 --> 00:07:24.000 And there's a couple of ways to go about this. 00:07:24.000 --> 00:07:39.000 So before an earthquake the ground surface is flat and directly after an earthquake, it creates a scarf here, and this scarf or roads over time and traps things like charcoal from forest fires and other organic matter in the sediments and we call this 00:07:39.000 --> 00:07:51.000 the colonial wedge and settlements in organic matter that are trapped in here can be carbon dated, and that gives us a maximum age for the most recent earthquake on this fault. 00:07:51.000 --> 00:08:03.000 So our primary methodology for determining the age of the most recent earthquake is going to rely on carbon 14 agents from charcoal and other organic matter trapped in these colonial wedges along the length of the fault. 00:08:03.000 --> 00:08:16.000 So we're going to end up collecting charcoal from locations along default and do carbon dating this is another location. This is called Graham Creek with these more of these beautiful glacial Marines flanking the sides of this canyon. 00:08:16.000 --> 00:08:26.000 And we're going to use those to estimate the age of the most recent earthquake, but we're also going to use cosmic gigantic exposure dating to determine the age of glacial seven settlements and deposits. 00:08:26.000 --> 00:08:33.000 So this glacial moraine here, this deposit that was sort of pushed to the side by ice this whole Canyon would have been filled by ice. 00:08:33.000 --> 00:08:49.000 We can use the rocks in this morning to determine how long it's been exposed to the sky, basically to sunlight cosmic rays interact with minerals and elements in the rock, create helium three which is an isotope of Helium, and that determines how long 00:08:49.000 --> 00:08:55.000 the rock has been exposed. So like right here at the end, the top end of the Morena where it needs to cliff. 00:08:55.000 --> 00:08:59.000 There's a considerably larger offset here about six meters. 00:08:59.000 --> 00:09:06.000 And this could be from multiple earthquakes, but determining how much offset has occurred here. 00:09:06.000 --> 00:09:10.000 After we determine the age of this glacial moraine here. 00:09:10.000 --> 00:09:22.000 That gives us a long term slip rate for this fall, or how fast is this fault move over time. And that could be anywhere from the order of a half a millimeter per year to 10 millimeters per year. 00:09:22.000 --> 00:09:40.000 Now it's not likely to be 10 millimeters per year here but just for an example, and its fastest the San Andreas Fault moves about 40 millimeters per year, whereas false here in this part of Oregon, probably move closer to point five millimeters per year. 00:09:40.000 --> 00:09:54.000 So a lot of this research is going to be based on fieldwork I'm going to end up spending about three weeks out on the strawberry mountains, the beautiful strawberry mountains, this is a rendering from Google Earth showing the strawberry mountains in 3d 00:09:54.000 --> 00:10:07.000 with my fault traces here going along the mountain front, and we're going to be hiking cross country a lot of the time just to verify the measurements that I'm taking from the LIDAR base map and collecting rock samples to determine locals photography, 00:10:07.000 --> 00:10:11.000 you can see these lava layers here in the cliff. 00:10:11.000 --> 00:10:19.000 So we're going to verify that those are in fact the rocks that we think they are. And, and perhaps do some limited chemistry work on them to identify them. 00:10:19.000 --> 00:10:35.000 We will definitely be collecting rock chips for cosmic dating from glacial sediments and deposits, and we're going to be doing auger core trans sex, which is essentially digging holes across the scarf to recover charcoal from those colonial wedge settlements, 00:10:35.000 --> 00:10:41.000 and those will give us our carbon 14 samples for bracketing the age of this earthquake. 00:10:41.000 --> 00:10:58.000 So are anticipated results, including a geologic strip maps that are on the fault. This area has been mapped previously by geologists but at a very large scale meeting in a very zoomed out view but I'm going to be taking a much more zoomed in closer look 00:10:58.000 --> 00:11:07.000 at this fall and the rocks around it. So I'm going to create a narrow map along the link to this fault, which shows the rocks and other structures present there. 00:11:07.000 --> 00:11:14.000 We're also going to find displacement measurements along the strike of the fault, so how much the fault has moved across the length of it. 00:11:14.000 --> 00:11:28.000 And because majestic issues of these glacial features is going to be a first not only for the strawberry mountains but really for this whole region of the Blue Mountains in Oregon, and that will give glaciologists and climatologists a much better, a higher 00:11:28.000 --> 00:11:38.000 resolution view of glaciology and the way these Alpine glaciers behaved in Oregon, in the last ice age. 00:11:38.000 --> 00:11:51.000 And we're also going to compare the data we find on this fault to other faults in the area, notably the brothers fault zone, or the Unity base and faults or a number of other geologic faults that are in this area. 00:11:51.000 --> 00:12:05.000 But most importantly, for me, the most important aspect of this Reacher's research is determining whether or not this fall is in fact recently active and therefore does it pose a hazard to the people that live in the john a valley. 00:12:05.000 --> 00:12:19.000 That's the main question of this research as far as I'm concerned, I'm not going to determine whether or not, like, I'm not going to be doing, not going to be modeling earthquake events in determining ground motion, like they do for other earthquakes. 00:12:19.000 --> 00:12:29.000 But just determining whether or not this fault is active by finding out how long ago it produced its most recent earthquake is extremely important to the people of Eastern Oregon. 00:12:29.000 --> 00:12:45.000 Here are some of my work cited you may pause the video and take a look at those. If you're curious. And here's my timeline of my research and my budget, and if you have any questions, please email me at a dunning@pdx.edu and check out my YouTube channel, 00:12:45.000 --> 00:13:15.000 better geology, where I will be covering my research as time goes forward over the last about six months I've been accumulating background research and sort of accumulating it target areas of interest along this study area.