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[Music]

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good morning everyone

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um we're at the awesome my name is

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Andrea Brian I'm a PhD student at

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University Chicago and today I will talk

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about investigating the use of long

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period seismology to explore Titan's

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interior I'm aware that

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um I'm actually quite new to seismology

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myself when we began a couple years ago

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so I will try to do a little bit of

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background for everyone all right so

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starting with Cassini we learned a lot

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about the saturnian system but

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especially for this study we learned a

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lot about Titan and so

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um there was actually a probe the

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hoyigan's probe that landed on the

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surface of Titan and you can if you go

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on YouTube you can Google it and or you

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can YouTube it and see the landing um

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there it's leaning through the haze and

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you see some water ice Pebbles on the

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surface

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um and there's so much I could say about

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Titan but for the sake of time I'll just

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say it's an amazing natural astrobiology

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Laboratory

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um and um

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I'm very excited to do some theory about

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it

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um okay so here is what we currently

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know about Titan

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um and so we know that there is a liquid

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water ocean underneath

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um a very thick shell of ice so it's

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between 50 and 150 kilometers deep

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um we don't know the exact compositions

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of this ice shell or the ocean but we do

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know that there's water there

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um and also there could be some high

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pressure ice underneath the ocean and

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this actually has very big

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astrobiological implications because it

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could actually act if there is high

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pressurized it could act as a barrier

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from there's the enrichment of the ocean

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for potential life

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um if it's there and so

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um yeah so that's something that

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seismology can help us to constrain

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whether or not that's there

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um okay so this brings me to NASA

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dragonfly and to dragonfly

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um is a rotor craft that will launch in

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2027

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um and it'll take about six years or so

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to get to Titan

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um but this instrument will be loaded

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with many many different instrument

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packages that are really there's a very

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large Focus for Astro bio and in

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particularly the seismometer

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um which is going to be on the other

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Underside you can see here it's like

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dangling or it's up under the rotocraft

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but it's going to be tethered it's

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tethered and so it'll be lowered down at

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each location on Titan that's going to

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visit and then measure the seismic

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activity there and there also these

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geophones which are essentially less

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sensitive seismometers and they're a bit

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smaller that are going to be there's two

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under the underside of the skids and so

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in particular the seismometer the

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geophones and other instruments within

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the this drag map package are going to

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be looking to measure habitability

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okay so um dragonfly says melody

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seismology in a nutshell will help us to

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constrain the interior structure of

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Titan more precisely and so seismology

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um similarly like on Earth has helped us

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to understand more about the actual

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interior of Earth

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um to like very great detail and so we

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hope to be able to do a bit of the same

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um on Titan and so some possible causes

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of Titan Quakes will be tidal flexing or

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Quail volcanoes and then also like ice

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cracking events of various kinds and

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this is of course not a non-exhaustive

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list and so we'll be able to put like

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very precise

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um more precise hopefully measurements

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on what's actually going on there okay

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so now this brings me to the namesake of

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this talk long period seismology so

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um I'm talking about so if you're

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familiar with seismograms we have the

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Body Waves or those are the p waves

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compressive waves and the sheer waves S

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waves and then we have

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um later on we have these long these

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surface waves and so I'm looking as

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opposed to using Body Waves

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investigating

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um and particularly with these I'm

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looking at methane cloth rate models

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what if I were to use the surface wave

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information particularly dispersion

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information to be able to try to learn

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about Titan and maybe about the

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eyeshadow thickness so let's see what I

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found okay so starting with methane

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clathrates

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um I for those of you don't know what

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that is

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um so a clothway is essentially I like

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to say a water cage and so you can see

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um I don't know if you can see those

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um this is essentially

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um a structure of water molecules around

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and they're entrapping a single molecule

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and and the case of or in my the study

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the molecule we're looking at would be

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methane okay so imagine there's this

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molecule and now we have tens of

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kilometers of this these methane

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clathrates and we think that this could

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be very possible and very plausible for

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the Titan for Titan conditions um and I

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think I forgot to mention Titan surface

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is 94 Kelvin so on the surface methane

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we have a hydrological cycle but it's a

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methane hydrological cycle

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um six percent or five or six percent of

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the atmosphere is methane

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um and so we have instead of lakes of

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water lakes of hydrocarbons

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um and lakes of methane

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um

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so

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um when we have this liquid methane and

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ice under Titan temperatures and

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pressures they will readily form these

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methane clathrates and it's been shown

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in the laboratory so it's thought that

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they're most likely will be lots of

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these methane clathrates on Titan

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um and so the models that we considered

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um were essentially they were all the

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same so we were looking at 100 kilometer

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thick ice shell and just varying the um

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the clathrated lid thickness so um the

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cloth grades were just at the surface so

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hence the cloth rate lid

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um and um yeah these are all spherically

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symmetric models they were generated

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with an open source code called Planet

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profile if you're interested in

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generating this it's on GitHub also you

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can I couldn't show you how to get it or

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you can just Google it

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um and there's a ton of other bodies you

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can look at there as well and so we

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simulated a magnitude 3 quick and then

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these were the data that we'll be

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looking at come from a three kilometer

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Source step so three kilometers deep

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within the ice

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Okay so so um

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the from the study

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um I this was led by Angela marusiak at

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um who is now professor at University of

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Arizona uh and so we actually saw some

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small differences in dispersion between

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two of the models in particular that

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we're looking at and in that paper so

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that was the 10 kilometer cloth rate lid

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and the

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um pure water is shell and so just for

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this is a primer about dispersion it's

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related to the material properties of

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the ice shell and particularly in the

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case of elastic waves that we're looking

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at here and so this wave speed depends

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on frequency and that's kind of like the

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meat of what dispersion is is seeing how

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the wave speed or the group velocities

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they change as a function of frequency

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and so we saw like about two percent

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difference a two percent difference

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between the dispersion so that's looking

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at this group velocity curve here it's

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very small differences but they're small

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enough that if you have a really high

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Precision seismometer you could actually

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detect that which is actually I found

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that quite intriguing so I was like well

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let's dig deeper and see what else we

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can find

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um so this brings me to the setup of the

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um on the project of this long period

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study that I'm leading now so

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um I take theoretical dispersion curves

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so it's all theoretical but these are

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extra theoretical

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um and I can explain what that means

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later

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um or if you if you ask um so

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theoretical this version curve they're

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generated with a code called mineos and

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elaborate on that and then take these

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other axi Simmons it says that's another

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code so the different methods of doing

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these things

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um seismograms to create these mock

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observational data of which I would go

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and pick and calculate by hand

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um and with a computer the group

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velocities for each Titan input model

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I'm not sure that I'm across a range of

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distances um and frequencies so

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um now just I'll talk about the

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theoretical group velocities

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um and so these are looking at group

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velocity as a functional frequency so

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group velocity on the y-axis and

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frequency on the X axes and I'm looking

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at different modes so I'll talk about

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what the screw velocities and phase

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velocities are and or group velocities

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are and then what the modes are

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um so group velocity

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um if we were to look if you look on the

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right hand side it's

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um the the actual velocity of the like

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wave packet that's encapsulating the

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like more the bigger larger scale

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structure of our seismograms and the

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phase velocities that's another measure

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of dispersion

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um it is the actual velocity of the

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Peaks and so when you have the groove

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velocity not equal to the phase velocity

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you you know you have a dispersive wave

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um and so

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um

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the terminal information so mode so if

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if you remember from physics the like

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wave on the string analogy

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um or it's not analogy but the wave on a

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string representation of modes

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um the fundamental modes will be here

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there's no node first overturn one node

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second third second and two and three

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nodes uh accordingly or respectively and

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then you can go all the way up to I mean

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as many nodes and modes as you'd like to

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um so for this study we actually looked

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at up to three thousand uh overtones to

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create an entire seismogram but here

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um we know that most of the information

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of this surface wave that we're looking

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at and I forgot to mention that it's a

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Rayleigh wave

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um it was it would normally be in the

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fundamental mode but

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um there's a surprise that I'll show you

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in the next slide

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um

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and so essentially what we found was

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that when we're comparing

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um when we're looking at the data and I

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I went and used actually some this other

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data set

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um and took the seismograms themselves

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and

281
00:10:25,430 --> 00:10:24,000
um calculated the group velocities as

282
00:10:27,590 --> 00:10:25,440
opposed to just them being spit out from

283
00:10:29,930 --> 00:10:27,600
a code for me

284
00:10:32,690 --> 00:10:29,940
um consistently that

285
00:10:33,710 --> 00:10:32,700
um the dispersion profiles um there when

286
00:10:36,050 --> 00:10:33,720
we look at the different interior

287
00:10:37,730 --> 00:10:36,060
structures they do like differ slightly

288
00:10:39,530 --> 00:10:37,740
but then when we lay them on top of each

289
00:10:41,509 --> 00:10:39,540
other essentially like there isn't

290
00:10:43,430 --> 00:10:41,519
various little differences and it's so

291
00:10:44,690 --> 00:10:43,440
small that you probably would not and

292
00:10:47,110 --> 00:10:44,700
not probably wouldn't they would be

293
00:10:49,430 --> 00:10:47,120
smaller than what we could observe

294
00:10:52,069 --> 00:10:49,440
on Titan

295
00:10:53,750 --> 00:10:52,079
um so and then also the Israeli waves we

296
00:10:55,190 --> 00:10:53,760
thought that they would be the

297
00:10:56,870 --> 00:10:55,200
information would be in the fundamental

298
00:10:58,730 --> 00:10:56,880
mode but actually it was in the first

299
00:11:00,769 --> 00:10:58,740
overtone which is a little interesting

300
00:11:02,449 --> 00:11:00,779
and it's consistently so that okay so

301
00:11:05,090 --> 00:11:02,459
there's this yellow line is the first

302
00:11:07,910 --> 00:11:05,100
overtone and so this blue little Cloud

303
00:11:09,829 --> 00:11:07,920
thing is the one Sigma standard

304
00:11:12,410 --> 00:11:09,839
deviation from these group velocity

305
00:11:15,590 --> 00:11:12,420
measurements which are taken over a

306
00:11:18,110 --> 00:11:15,600
range of just instances and frequencies

307
00:11:20,630 --> 00:11:18,120
um and so

308
00:11:22,970 --> 00:11:20,640
um yeah it's it's a pretty pretty strong

309
00:11:25,790 --> 00:11:22,980
uh thing that's happening or signal that

310
00:11:27,230 --> 00:11:25,800
we're seeing for it not being and the

311
00:11:29,630 --> 00:11:27,240
fundamental mode

312
00:11:30,590 --> 00:11:29,640
um and so then that just shows that this

313
00:11:33,530 --> 00:11:30,600
method

314
00:11:34,610 --> 00:11:33,540
um we wouldn't be able to use Body Waves

315
00:11:37,430 --> 00:11:34,620
to

316
00:11:39,470 --> 00:11:37,440
um this sorry the surface wave this

317
00:11:41,210 --> 00:11:39,480
particular surface wave as

318
00:11:44,930 --> 00:11:41,220
um to diagnose the thickness of Titan's

319
00:11:49,550 --> 00:11:44,940
eyeshadow so that's intriguing and so

320
00:11:52,190 --> 00:11:49,560
um I will dig deeper and and see

321
00:11:53,810 --> 00:11:52,200
um more about that in the future all

322
00:11:55,850 --> 00:11:53,820
right so a quick summary I use data

323
00:11:57,710 --> 00:11:55,860
driven models of Titan's Interiors or to

324
00:11:59,690 --> 00:11:57,720
compute Titan synthetic seismograms for

325
00:12:01,970 --> 00:11:59,700
comparison to real data that we'll get

326
00:12:03,769 --> 00:12:01,980
from dragonfly in the mid-2030s and in

327
00:12:05,090 --> 00:12:03,779
the study we investigate energy chat

328
00:12:07,069 --> 00:12:05,100
trapped in the eye shell to determine

329
00:12:09,350 --> 00:12:07,079
the structure of Titan and the presence

330
00:12:11,810 --> 00:12:09,360
of surface clathrates

331
00:12:14,269 --> 00:12:11,820
um and AKA long period seismology And

332
00:12:15,590 --> 00:12:14,279
while the surface waves observation that

333
00:12:18,050 --> 00:12:15,600
we saw in the study do not clearly

334
00:12:20,210 --> 00:12:18,060
determine thickness we can constrain it

335
00:12:21,230 --> 00:12:20,220
using body wave arrivals so P and S

336
00:12:22,970 --> 00:12:21,240
waves and if you're interested in

337
00:12:24,829 --> 00:12:22,980
learning more about isolation seismology

338
00:12:27,410 --> 00:12:24,839
and particularly about some of the

339
00:12:29,449 --> 00:12:27,420
methodology that we were implementing

340
00:12:32,930 --> 00:12:29,459
talk to me or also consult Simon

341
00:12:35,630 --> 00:12:32,940
staler's paper uh it's very looking also

342
00:12:37,670 --> 00:12:35,640
at other icy ocean worlds as well and

343
00:12:39,410 --> 00:12:37,680
then understanding the composition of

344
00:12:40,910 --> 00:12:39,420
Titan's interior especially the ice

345
00:12:43,129 --> 00:12:40,920
shell and ocean will have important

346
00:12:45,230 --> 00:12:43,139
implications for astrobiology and

347
00:12:50,730 --> 00:12:45,240
habitability studies so thank you so

348
00:12:50,740 --> 00:13:03,290
[Music]

349
00:13:10,970 --> 00:13:05,509
all right

350
00:13:15,949 --> 00:13:13,129
hi nice talk

351
00:13:16,910 --> 00:13:15,959
um so presumably like in the lab we

352
00:13:19,250 --> 00:13:16,920
don't have

353
00:13:21,889 --> 00:13:19,260
like kilometers of class rates so what

354
00:13:25,069 --> 00:13:21,899
does it take to extrapolate from just

355
00:13:26,870 --> 00:13:25,079
this lab made amount to how it'll behave

356
00:13:29,569 --> 00:13:26,880
when it's this much

357
00:13:32,569 --> 00:13:29,579
um as a medium yeah so we use this paper

358
00:13:34,509 --> 00:13:32,579
called by calasova and soton I think

359
00:13:36,230 --> 00:13:34,519
it's in like 20

360
00:13:38,509 --> 00:13:36,240
20.

361
00:13:39,949 --> 00:13:38,519
um but that was their paper is where we

362
00:13:42,350 --> 00:13:39,959
got the actual thermal

363
00:13:54,530 --> 00:13:42,360
um thermal models to model to model this

364
00:13:57,949 --> 00:13:56,150
thank you for the talk

365
00:14:01,310 --> 00:13:57,959
um I I have a question that may be

366
00:14:03,290 --> 00:14:01,320
outside of the scope of what you do but

367
00:14:06,290 --> 00:14:03,300
um I know that the eye shelf thickness

368
00:14:10,310 --> 00:14:06,300
can be a proxy for for heat loss and

369
00:14:12,650 --> 00:14:10,320
that can also kind of um uh

370
00:14:14,690 --> 00:14:12,660
provide clues as to whether the ocean

371
00:14:17,030 --> 00:14:14,700
may be like a transient feature like a

372
00:14:19,430 --> 00:14:17,040
more long-lived feature is that anything

373
00:14:21,069 --> 00:14:19,440
you can determine using the data that

374
00:14:23,750 --> 00:14:21,079
may be

375
00:14:25,610 --> 00:14:23,760
collected by dragonfly or anything like

376
00:14:28,310 --> 00:14:25,620
that or is that outside of the scope of

377
00:14:30,590 --> 00:14:28,320
because I mean the the longevity of the

378
00:14:32,150 --> 00:14:30,600
ocean like if there is like a like a

379
00:14:34,009 --> 00:14:32,160
liquid water ocean

380
00:14:35,449 --> 00:14:34,019
um beneath the ice layers that could

381
00:14:36,949 --> 00:14:35,459
have implications in the habitability

382
00:14:38,990 --> 00:14:36,959
whether it's like persisted over

383
00:14:43,189 --> 00:14:39,000
geologic time scales

384
00:14:45,889 --> 00:14:43,199
yeah I mean I mean we can constrain the

385
00:14:50,030 --> 00:14:45,899
with just what size seismology the

386
00:14:51,530 --> 00:14:50,040
composition and the depth but regarding

387
00:15:03,170 --> 00:14:51,540
yeah it's a little bit outside of my

388
00:15:05,990 --> 00:15:05,269
yeah uh so I'm curious

389
00:15:07,910 --> 00:15:06,000
um

390
00:15:09,650 --> 00:15:07,920
what is the amount of confidence we have

391
00:15:11,810 --> 00:15:09,660
that there's a high pressure ice layer

392
00:15:14,389 --> 00:15:11,820
on the bottom instead of you know a

393
00:15:16,850 --> 00:15:14,399
direct contact with the ocean yeah I

394
00:15:19,310 --> 00:15:16,860
mean we don't have like any confidence

395
00:15:21,530 --> 00:15:19,320
to say I mean

396
00:15:22,910 --> 00:15:21,540
um we think that there could be

397
00:15:27,050 --> 00:15:22,920
um I think there's

398
00:15:29,030 --> 00:15:27,060
definitely a big Camp thinking there is

399
00:15:31,670 --> 00:15:29,040
um but it's highly debatable so if I

400
00:15:33,829 --> 00:15:31,680
were to like look at that diagram

401
00:15:34,910 --> 00:15:33,839
um I could put a big sorry going way

402
00:15:37,490 --> 00:15:34,920
back

403
00:15:38,810 --> 00:15:37,500
um there

404
00:15:40,129 --> 00:15:38,820
um for the high pressure eyes you could

405
00:15:42,050 --> 00:15:40,139
put like a big question mark there

406
00:15:43,370 --> 00:15:42,060
because we don't know if it's there we

407
00:15:45,170 --> 00:15:43,380
don't know how thick it is it's like

408
00:15:48,410 --> 00:15:45,180
really deep down we know there's no

409
00:15:50,329 --> 00:15:48,420
molten core in Titan from some Casini

410
00:15:52,009 --> 00:15:50,339
measurements but high pressure rise we

411
00:15:54,650 --> 00:15:52,019
have a zero idea

412
00:15:56,449 --> 00:15:54,660
um but it could be there

413
00:15:57,889 --> 00:15:56,459
um and so especially because it's so

414
00:16:00,350 --> 00:15:57,899
cold but then

415
00:16:02,269 --> 00:16:00,360
yeah and if it is there there's

416
00:16:04,069 --> 00:16:02,279
different scenarios also that if we have

417
00:16:06,410 --> 00:16:04,079
porous high pressure eyes and it's

418
00:16:07,550 --> 00:16:06,420
really saline and then it could still

419
00:16:09,170 --> 00:16:07,560
um we could still have some enrichment

420
00:16:11,389 --> 00:16:09,180
of the ocean so even if it is there

421
00:16:13,370 --> 00:16:11,399
depending on its composition they could

422
00:16:15,350 --> 00:16:13,380
still be enrichment of the ocean

423
00:16:18,530 --> 00:16:15,360
um so it may not necessarily be a

424
00:16:32,569 --> 00:16:18,540
barrier to life also if it is there

425
00:16:37,249 --> 00:16:35,329
hi nice talk I would like to ask you if

426
00:16:39,889 --> 00:16:37,259
you have considered the influenza of the

427
00:16:41,810 --> 00:16:39,899
titleistic patient in your models always

428
00:16:43,970 --> 00:16:41,820
the title dissipation

429
00:16:45,829 --> 00:16:43,980
oh do I incorporate that if you have

430
00:16:48,170 --> 00:16:45,839
considered that influence in the

431
00:16:50,509 --> 00:16:48,180
generation of a Titan earthquake Titan

432
00:16:53,090 --> 00:16:50,519
Quake sorry so have you considered the

433
00:16:54,650 --> 00:16:53,100
influenza of the tidal dissipation

434
00:16:56,030 --> 00:16:54,660
um no we're not considering tidal

435
00:16:58,430 --> 00:16:56,040
dissipation

436
00:17:01,249 --> 00:16:58,440
um in the models or we're assuming it's

437
00:17:02,870 --> 00:17:01,259
a very perfect Titan but I also don't

438
00:17:04,309 --> 00:17:02,880
think

439
00:17:07,429 --> 00:17:04,319
um we're assuming we're considering

440
00:17:10,789 --> 00:17:07,439
attenuation within the ice shell but

441
00:17:14,710 --> 00:17:13,130
um we're not really thinking about I

442
00:17:19,329 --> 00:17:14,720
think and I don't think we need to yeah

443
00:17:26,090 --> 00:17:23,270
about earthquake if you

444
00:17:28,549 --> 00:17:26,100
um synthesize the sex meet analysis and

445
00:17:31,490 --> 00:17:28,559
the influencing of the television so um

446
00:17:34,669 --> 00:17:31,500
I don't know how much is a contribution

447
00:17:37,789 --> 00:17:34,679
of the Titan so that's why I am asking

448
00:17:39,529 --> 00:17:37,799
you if you have considered this um we

449
00:17:49,150 --> 00:17:39,539
haven't considered this parameter in

450
00:17:53,930 --> 00:17:52,789
yeah I don't know if it has like a huge

451
00:17:55,909 --> 00:17:53,940
um

452
00:17:58,549 --> 00:17:55,919
so so the title

453
00:18:00,650 --> 00:17:58,559
I don't think I will have uh like a

454
00:18:03,169 --> 00:18:00,660
large effect which is why we've left it

455
00:18:05,210 --> 00:18:03,179
out yeah yeah also that bang of the

456
00:18:07,190 --> 00:18:05,220
distance between the Titan and sat or so

457
00:18:12,650 --> 00:18:07,200
yeah I don't know that's why I was

458
00:18:18,890 --> 00:18:15,289
one more question

459
00:18:21,890 --> 00:18:18,900
so uh um I'm not a planetary geologist

460
00:18:23,270 --> 00:18:21,900
but I I do know that one of the

461
00:18:24,770 --> 00:18:23,280
limitations for our understanding of the

462
00:18:26,810 --> 00:18:24,780
interior of Mars with the Insight

463
00:18:28,789 --> 00:18:26,820
mission was that we only had a single

464
00:18:31,549 --> 00:18:28,799
seismometer yeah

465
00:18:33,650 --> 00:18:31,559
um in your data are you modeling uh

466
00:18:35,570 --> 00:18:33,660
basically seismology

467
00:18:37,730 --> 00:18:35,580
being measured by a single seismometer

468
00:18:39,350 --> 00:18:37,740
and you think having multiple

469
00:18:41,390 --> 00:18:39,360
seismometers on the surface of Titan

470
00:18:42,890 --> 00:18:41,400
would give you further resolution in

471
00:18:44,630 --> 00:18:42,900
terms of the thickness of methane

472
00:18:48,529 --> 00:18:44,640
clathrate lid

473
00:18:52,430 --> 00:18:48,539
yeah 100 it would be amazing to have

474
00:18:54,770 --> 00:18:52,440
multiple seismometers on Mars also on

475
00:18:56,750 --> 00:18:54,780
Titan but I think just with experimental

476
00:18:59,990 --> 00:18:56,760
Mission constraints like they can only

477
00:19:02,270 --> 00:19:00,000
have one have you done any modeling to

478
00:19:05,510 --> 00:19:02,280
see if you could get further resolution

479
00:19:07,190 --> 00:19:05,520
with multiple seismometers

480
00:19:10,370 --> 00:19:07,200
um so it's not so it's not really about

481
00:19:11,810 --> 00:19:10,380
like getting the resolution with

482
00:19:13,610 --> 00:19:11,820
um so we can generate perfect

483
00:19:16,130 --> 00:19:13,620
seismograms

484
00:19:18,770 --> 00:19:16,140
um it's just how well we'll be able to

485
00:19:20,990 --> 00:19:18,780
see and detect

486
00:19:23,270 --> 00:19:21,000
um things I see it's easier to like

487
00:19:26,029 --> 00:19:23,280
triangulate events and things with um

488
00:19:29,150 --> 00:19:26,039
when you have multiple seismometers

489
00:19:31,310 --> 00:19:29,160
um but yeah we can essentially if we we

490
00:19:33,529 --> 00:19:31,320
could see like deeper events if we have

491
00:19:35,510 --> 00:19:33,539
more seismometers we'd have just greater

492
00:19:38,150 --> 00:19:35,520
sensitivity overall

493
00:19:40,669 --> 00:19:38,160
um but we unfortunately don't have that

494
00:19:44,330 --> 00:19:40,679
yeah so we have to do what we can with

495
00:19:44,340 --> 00:19:50,380
thank you Andrea yeah

496
00:19:53,890 --> 00:19:51,610
[Music]