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0 Master's Thesis the Department of Geosciences And Master’s thesis The Department of Geosciences and Geography Physical Geography South American subduction zone processes: Visualizing the spatial relation of earthquakes and volcanism at the subduction zone Nelli Metiäinen May 2019 Thesis instructors: David Whipp Janne Soininen HELSINGIN YLIOPISTO MATEMAATTIS-LUONNONTIETEELLINEN TIEDEKUNTA GEOTIETEIDEN JA MAANTIETEEN LAITOS MAANTIEDE PL 64 (Gustaf Hällströmin katu 2) 00014 Helsingin yliopisto 0 Tiedekunta/Osasto – Fakultet/Sektion – Faculty Laitos – Institution – Department Faculty of Science The Department of Geosciences and Geography Tekijä – Författare – Author Nelli Metiäinen Työn nimi – Arbetets titel – Title South American subduction zone processes: Visualizing the spatial relation of earthquakes and volcanism at the subduction zone Oppiaine – Läroämne – Subject Physical Geography Työn laji – Arbetets art – Level Aika – Datum – Month and year Sivumäärä – Sidoantal – Number of pages Master’s thesis May 2019 82 + appencides Tiivistelmä – Referat – Abstract The South American subduction zone is the best example of an ocean-continent convergent plate margin. It is divided into segments that display different styles of subduction, varying from normal subduction to flat-slab subduction. This difference also effects the distribution of active volcanism. Visualizations are a fast way of transferring large amounts of information to an audience, often in an interest-provoking and easily understandable form. Sharing information as visualizations on the internet and on social media plays a significant role in the transfer of information in modern society. That is why in this study the focus is on producing visualizations of the South American subduction zone and the seismic events and volcanic activities occurring there. By examining the South American subduction zone it may be possible to get new insights about subduction zone processes. A particular point of interest is the relation of volcanoes and earthquakes to the trench, or in other words examining how far from the trench do they typically form or occur. To present this, a set of models, figures and animations were created using the Python programming language in Jupyter Notebooks. These notebooks utilize freely available software and aim to be easily understandable, reproducible and modifiable. For earthquakes, data from the United States Geological Survey (USGS) between January 1960 – December 2017, and for volcanoes, data from the Smithsonian institution covering the Holocene were used. Three main visualizations were created: 1) an animation of all of the earthquakes occurring chronologically, where bar plots show their frequency according to every two degrees of latitudes, and their location and magnitude is shown on a map, 2) a cross-section view of the sinking slab’s seismic structure on a selected latitude range, and 3) a static figure, which can portray several different aspects of earthquakes or volcanism, and their distribution on the South American margin using bar plots and a map. The visualizations show clearly the difference between segments of normal subduction compared to flat-slab subduction, especially in regard to volcanic activity or its absence. Visualizations also highlights the distribution of volcanoes and earthquakes, as across the margin volcanoes are present in areas where normal or transitional subduction is taking place and missing in flat-slab segments, and earthquakes occur at depths between 0 – 600 km, and 0 – 1300 km distance from the trench. Deep earthquakes remain an important topic of interest, as little is known of them, and their study remains challenging. In many segments, seismic gaps, which are another topic of interest, are also present at depths between 300 – 500 km. In conclusion, visualizations are an effective way of relaying large datasets in a way that is easy and fast to absorb, and make observation from. These models, figures and animations are useful especially due to their configurability, and can be shared to others to use in future works. Avainsanat – Nyckelord – Keywords South American subduction zone, earthquake, volcanism, subduction zone, flat-slab subduction, visualizations, model 1 Tiedekunta/Osasto – Fakultet/Sektion- Faculty Laitos – Institution – Department Matemaattis-Luonnontieteellinen tiedekunta Geotieteiden ja maantieteen laitos Tekijä – Författare – Author Nelli Metiäinen Työn nimi – Arbetets titel – Title South American subduction zone processes: Visualizing the spatial relation of earthquakes and volcanism at the subduction zone Oppiaine – Läroämne – Subject Luonnonmaantiede Työn laji – Arbetets art – Level Aika – Datum – Month and year Sivumäärä – Sidoantal – Number of pages Pro gradu Toukokuu 2019 82 + liitteet Tiivistelmä – Referat – Abstract Etelä-Amerikan alityöntövyöhyke on yksi parhaista esimerkeistä alityöntövyöhykkeistä, jossa merellinen ja mantereinen laatta liikkuvat toisiaan kohti. Lisäksi se on jakautunut useisiin lohkoihin, joissa alityöntövyöhyke käyttäytyy eri tavalla, erityisesti uppoavan laatan vajoamiskulman vaihdellessa normaalista matalaan. Tämä vaikuttaa vulkaaniseen toimintaan. Tiedon jakaminen on muuttumassa yhä visuaalisemmaksi, siksi tämä työ keskittyy Etelä- Amerikan alityöntövyöhykkeen, sekä siellä esiintyvien maanjäristysten ja vulkaanisten prosessien visualisoimiseen. Visualisoinnin avulla suurten tietomäärien välittäminen on nopeampaa, helpommin ymmärrettävää, ja usein myös kiinnostavampaa, kuin suurten tekstitiedostojen lukeminen. Tutkimalla Etelä-Amerikan alityöntövyöhykettä on mahdollista oivaltaa uusia asioita alityöntövyöhykkeistä. Eräs erityisen kiinnostuksen kohde on tulivuorten ja maanjäristysten suhde alityöntövyöhykkeeseen, toisin sanoen: kuinka kaukana, ja millä syvyydellä hautavajoamasta ne voivat esiintyä. Python ohjelmointikielellä luotiin helposti ymmärrettäviä, kopioitavia ja muunneltavia malleja, kuvia ja animaatioita Jupyter Notebook ohjelmistolla. Maanjäristyksiä varten käytettiin USGS:ltä saatavaa tiedostoa ajalta tammikuu 1960 – joulukuu 2017, tulivuoritoimintaa varten Smithsonian laitokselta tiedostoa, joka kattaa Holoseenin. Kolme pääasiallista mallia luotiin: 1) animaatio kaikista maanjäristyksistä kronologisesti, jossa pylväsdiagrammit esittelevät niiden jakautumista joka toisella leveysasteella pylväsdiagrammin avulla ja niiden sijainti ja magnitudi näkyvät kartalla, 2) läpileikkauskuva alityöntövyöhykkeiden seismisestä rakenteesta tiettyjen leveyspiirien välillä, ja 3) staattinen kuva, jossa voidaan esitellä maanjäristysten tai tulivuoritoiminnan tiettyä erityispiirrettä ja sen jakautumista Etelä- Amerikassa kartan avulla, sekä pylväsdiagrammeilla. Visualisoinnit osoittavat selvästi eron normaalin ja matalan alityönnön välillä, erityisesti vulkaaniseen toimintaan liittyen. Ne myös osoittavat tulivuoritoiminnan ja järistysten jakaantumisen selkeästi, tulivuoritoiminnan keskittyessä normaalin ja siirtymävaiheisen alityönnön alueilla. Järistyksiä esiintyy 0 – 650 km syvyydellä, ja 0 -1300 km etäisyyksillä hautavajoamasta. Järistysten esiintyminen suurissa syvyyksissä on edelleen keskeinen tutkimuksen aihe, sillä syvistä järistyksistä tiedetään vain vähän ja tutkimus on hankalaa. Myös alueella esiintyvät seismiset tauot (seismic gap) 300 – 500 km syvyydellä ovat tutkimusyhteisössä kiinnostava aihe. Visualisoinnit ovat tehokkaita suurten tietoaineistojen välittämisessä tavalla, jossa tieto on helposti ymmärrettävässä muodossa, ja havaintojen tekeminen on nopeaa. Tuotetut mallit sopivat hyvin jaettaviksi muulle tiedeyhteisölle ja kouluihin, erityisesti niiden helpon sovellettavuuden ja muokattavuuden vuoksi. Avainsanat – Nyckelord – Keywords Etelä-Amerikan alityöntövyöhyke, maanjäristys, tulivuoritoiminta, alityöntövyöhyke, visualisoinnit, mallinnus 2 TABLE OF CONTENTS ABSTRACT 1. INTRODUCTION .................................................................................................................................... 5 2. LITERATURE & THEORETICAL BACKGROUND ......................................................................................... 7 2.1 EARTH’S STRUCTURE ................................................................................................................................ 7 2.2 PLATE TECTONICS .................................................................................................................................... 8 2.2.1 THE HISTORY OF THE PLATE TECTONIC THEORY .................................................................................................... 8 2.2.2 THE IMPORTANCE OF TECTONIC PLATES ............................................................................................................. 9 2.3 SUBDUCTION ZONES .............................................................................................................................. 11 2.3.1 FORCES DRIVING SUBDUCTION ....................................................................................................................... 12 2.3.2 SUBDUCTION ZONE STRUCTURE ..................................................................................................................... 14 2.3.3 SUBDUCTION ZONE LIFECYCLE ........................................................................................................................ 19 2.3.4 FLAT-SLAB SUBDUCTION ............................................................................................................................... 21 2.4 EARTHQUAKES AT SUBDUCTION ZONES .....................................................................................................
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