Chiphunzitso Choyambirira ndi Kugwiritsa Ntchito Seismic Tomography
Kujambula kwa dziko lapansi pogwiritsa ntchito mafunde a seismic ndi njira ya geophysical yomwe imagwiritsidwa ntchito "kujambula" mkati mwa Dziko lapansi pogwiritsa ntchito mafunde a seismic. Mofanana ndi CT scan mu zamankhwala, yomwe imapanga chithunzi cha thupi la magawo atatu kuchokera ku X-ray, kujambula kwa seismic kumayesa kapangidwe ka pansi pa nthaka pogwiritsa ntchito deta ya nthawi yoyenda, amplitude, kapena ma waveforms olembedwa ndi netiweki ya seismometers. Njirayi ndi yofunika kwambiri chifukwa mkati mwa Dziko lapansi simungawonekere mwachindunji, pomwe mphamvu monga ma plate tectonics, zochitika za volcano, ndi zivomerezi zimakhudzidwa kwambiri ndi kusiyana kwa mawonekedwe a miyala pa kuya kwake.
1. Lingaliro Loyambira la Mafunde a Chivomerezi
Mafunde a chivomerezi ndi mafunde otambalala omwe amafalikira kudzera m'thanthwe. Mafunde a chivomerezi nthawi zambiri amagawidwa m'magulu awa:
1. Mafunde a thupi
– Mafunde a P (oyamba/opanikizika): amafalikira mofulumira kwambiri, amatha kudutsa mu zinthu zolimba ndi zamadzimadzi, amamva kusintha kwa liwiro la kupsinjika ndi kuchulukana.
– Mafunde a S (achiwiri/omwe amameta): ochedwa kuposa P, sangafalikire m'madzimadzi, ozindikira kuuma (kumeta modulus) kwa thanthwe.
2. Mafunde a pamwamba
Mwachitsanzo, mafunde a Rayleigh ndi Love, omwe nthawi zambiri amakhala otchuka kwambiri m'marekodi a zivomerezi zakutali, amakhala ofalikira, ndipo ndi othandiza kwambiri pa kapangidwe ka lithosphere mpaka ku asthenosphere yosaya.
Liwiro la mafunde a chivomerezi limadalira magawo otanuka (modulus) ndi kuchulukana. Kusintha kwa kutentha, kapangidwe ka mchere, kuthamanga, ma porosity, kusweka, ndi kupezeka kwa madzi kapena kusungunuka pang'ono kumakhudza liwiro. Ili ndiye maziko enieni ofotokozera kusiyana kwa liwiro kuti apereke zizindikiro za momwe zinthu zilili pansi pa nthaka.
2. Mfundo Zokhudza Tomography: Vuto Loyang'ana M'mbuyo ndi Vuto Lobwerera M'mbuyo
Kujambula kwa mafunde a seismic kumaphatikizapo mfundo ziwiri:
a) Vuto la kutsogolo (vuto la kutsogolo)
Popeza chitsanzo cha Dziko Lapansi (monga kugawa kwa liwiro la mafunde), titha kuwerengera kuneneratu kwa deta ya zivomerezi: nthawi yoyenda ya mafunde kuchokera ku gwero (chivomerezi kapena gwero lopangidwa) kupita ku siteshoni. Mu njira yosavuta yogwiritsira ntchito chiphunzitso cha mafunde, njira ya mafunde imaganiziridwa kuti ndi cheza chomwe chimatsatira mfundo ya Fermat: mafunde amasankha njira yokhala ndi nthawi yocheperako yoyendera.
Mwa masamu, nthawi yoyenda \(T\) ikhoza kulembedwa motere:
\[
T = \int_{\text{ray}} \frac{ds}{v(\mathbf{x})}
\]
kumene \(v(\mathbf{x})\) ndi liwiro la mafunde pamalo \(\mathbf{x}\), ndipo \(ds\) ndi chinthu cha kutalika kwa njira.
b) Vuto losiyana
Chosiyana ndi ichi: tili ndi deta yowonera (nthawi yoyenda, nthawi yoyenda, kufalikira kwa mafunde pamwamba, kapena mawonekedwe a mafunde) ndipo tikufuna kuyerekeza chitsanzo cha liwiro loyenera kwambiri. Vuto lotsutsana nthawi zambiri silili lapadera komanso losakhazikika: mitundu ingapo imatha kukwanira mofanana, ndipo detayo ili ndi kusatsimikizika/phokoso. Chifukwa chake, kukhazikika ndikofunikira, monga kusalala, kunyowa, kapena zoletsa za geology.
Mwachizolowezi, kusinthasintha nthawi zambiri kumachitika mwanjira yolunjika: chitsanzo choyamba chimasokonekera pang'ono, kenako kusiyana kwa nthawi yoyenda kumawerengedwa motere:
\[
\delta T \approx \int_{\text{ray}} \delta s(\mathbf{x})\, ds
\]
kumene \(\delta s = \delta(1/v)\) ndi kusokonezeka kwa kuchedwa. Ma equation awa amakonzedwa mu dongosolo lalikulu la mzere \( \mathbf{d} = \mathbf{Gm} \), kenako amathetsedwa ndi njira ya damped least squares kapena kusiyana kwake.
3. Mitundu ya Chivomerezi cha Dziko
1) Kujambula zithunzi nthawi yoyenda
Njira yodziwika kwambiri imagwiritsa ntchito kufika kwa P- ndi S-phase kuchokera ku zivomerezi zambiri. Deta ndi zotsalira za nthawi yoyenda poyerekeza ndi chitsanzo chofotokozera (monga, IASP91 kapena ak135 padziko lonse lapansi). Yoyenera kutengera chitsanzo cha liwiro la 3D mu crust ndi upper mantle, makamaka ngati netiweki ya siteshoni ndi yokhuthala.
2) Kujambula kwa mafunde a pamwamba
Pogwiritsa ntchito kufalikira (kusintha kwa gawo/kayendedwe ka gulu ndi nthawi) kwa mafunde a Rayleigh/Love. Popeza ndi ofooka kwambiri pa kapangidwe kake mpaka kapakatikati, tomography iyi ndi yothandiza kwambiri pojambula makulidwe a lithospheric, madera otsika kwambiri (LVZ), komanso kusintha kwa kutentha.
3) Teleseismic tomography (teleseismic tomography)
Kugwiritsa ntchito zivomerezi zakutali (teleseismic) zomwe mafunde ake amadutsa m'malo obisika kenako amajambulidwa ndi netiweki yakomweko. Ubwino wake: zili ndi magwero osiyanasiyana ndipo zimachokera mbali zosiyanasiyana, motero zimathandiza "kuunikira" kuchuluka kwa malo ophunzirira, mwachitsanzo pansi pa mapiri ophulika kapena madera otsetsereka.
4) Kujambula kwa mawonekedwe a waveform / kusinthasintha kwa mawonekedwe a waveform (FWI)
Pogwiritsa ntchito mawonekedwe athunthu a mafunde, osati nthawi yongofika yokha, mwachiphunzitso imapereka chidziwitso chapamwamba chifukwa imagwiritsa ntchito mokwanira chidziwitso cha amplitude ndi gawo, koma imafuna zofunikira zazikulu zamakompyuta ndi chitsanzo chabwino choyambirira kuti ipewe misampha yocheperako yapafupi.
4. Magawo Onse Ogwiritsira Ntchito ndi Kutembenuza
1. Kupeza deta
Kusonkhanitsa zojambula kuchokera ku ma seismometer okhazikika kapena osakhalitsa. Pa sikelo yofufuzira, gwero likhoza kukhala kuphulika kapena kugwedezeka; pa sikelo ya chigawo ndi dziko lonse lapansi, gwero lalikulu ndi chivomerezi.
2. Kuzindikira ndi kusankha gawo
Kudziwa nthawi yofika kwa mafunde a P, S, kapena pamwamba. Ubwino wa chotolacho umatsimikizira ubwino wa chitsanzocho.
3. Kukonza koyamba ndi kupanga chitsanzo
Kukonza nthawi (kusuntha kwa wotchi), kukonza kukwera, ndi kusankha chitsanzo chofotokozera. Chitsanzo choyamba chingakhale 1D kapena 3D yosavuta.
4. Kuyerekeza kwa mafunde ndi ma ray tracing/wave
Werengerani njira ya ma radiation opangidwa kapena ma waveforms kuti mupange sensitivity matrix.
5. Kusintha ndi kukhazikika
Kuthetsa dongosololi kuti mupeze chitsanzo cha liwiro. Kukhazikitsa malamulo kumasankhidwa kutengera cholinga: kaya kuwonetsa zolakwika zakuthwa kapena machitidwe osalala.
6. Kuwunika kwa mayankho ndi kuyesa kudalirika
Mwachitsanzo, pogwiritsa ntchito mayeso a checkerboard, mayeso a spike, kapena kusanthula kwa covariance/point spread function kuti muwone magawo omwe atsimikizika ndi deta.
5. Kutanthauzira kwa Chitsanzo cha Kuthamanga
Zotsatira za tomography nthawi zambiri zimakhala mapu a zolakwika za liwiro: madera okwera kwambiri nthawi zambiri amatanthauzidwa ngati miyala yozizira, yokhuthala, kapena yolimba (monga, ma subducting slabs). madera otsika kwambiri amatha kusonyeza kutentha kwambiri, miyala yosinthika, madera osweka odzaza ndi madzi, kapena kusungunuka pang'ono—nthawi zambiri kumagwirizanitsidwa ndi mapiri ophulika kapena hot asthenosphere.
Komabe, kutanthauzira kuyenera kusamala chifukwa liwiro limakhudzidwa ndi zinthu zambiri. Mwachiyembekezo, seismic tomography imaphatikizidwa ndi deta ina monga mphamvu yokoka, magnetotelluric (MT), geodesy, surface geology, ndi petrology.
6. Ntchito za Seismic Tomography
a) Kuphunzira za madera ocheperako ndi mphamvu za mbale
Kujambula kwa dziko lonse ndi dera lonse kumatha kujambula slab yozungulira mantle, kuphatikizapo mawonekedwe ake, kuya kwake, ndi kugawika kwake. Izi ndizofunikira kwambiri pomvetsetsa magwero a zivomerezi zazikulu, njira zolumikizirana kwa mbale, komanso kusintha kwa tectonic kwa dera.
b) Machitidwe a mapiri ophulika ndi kuchepetsa masoka
M'madera ophulika, tomography imatha kuzindikira madera otsika kwambiri okhudzana ndi zipinda za magma, njira zokwera zamadzimadzi, kapena miyala yosinthika. Ndi kuyang'aniridwa pafupipafupi, kusintha kwa liwiro (time-lapse tomography) kungapereke zizindikiro za kayendedwe ka madzi/magma koyenera kuti pakhale chenjezo loyambirira la kuphulika.
c) Kufufuza mphamvu ndi zinthu
Pa sikelo yosaya kwambiri ya crustal, tomography imagwiritsidwa ntchito pofufuza za hydrocarbon, geothermal, ndi migodi. Kusintha kwa liwiro kumathandiza kuyika mapu a lithology, kapangidwe ka zolakwika, madera osweka, ndi malo osungiramo madzi. Mu geothermal, kuphatikiza kwa tomography ndi MT nthawi zambiri kumakhala kothandiza: tomography imapereka chidziwitso chotanuka, MT imapereka chidziwitso cha fluid conductivity.
d) Kufotokozera za zolakwika zomwe zikuchitika komanso zoopsa za chivomerezi
Kujambula kwa malo kumatha kuwonetsa madera ofooka, madera owonongeka, ndi kusiyana kwa zolakwika. Izi zimathandiza kumvetsetsa kugawika kwa zolakwika, kutsekeka komwe kungatheke, ndi kusintha kwa liwiro komwe kumakhudza kukulitsa kwa mafunde (zotsatira za malo).
e) Kapangidwe ka crustal ndi lithospheric m'chigawo
Pogwiritsa ntchito tomography ya mafunde a pamwamba, ofufuza amatha kujambula makulidwe a lithospheric, malire a Moho, ndi zolakwika za asthenospheric. Zotsatirazi ndizomwe zimapangitsa kuti pakhale zitsanzo za geodynamic, kuphatikizapo mapangidwe a beseni, orogenesis, ndi kusintha kwa kontinenti.
7. Zolepheretsa ndi Zovuta
Kujambula kwa mafunde a dziko lapansi kumadalira kwambiri kufalikira kwa magwero ndi malo owonetsera. Madera omwe ali ndi zivomerezi zochepa kapena malo ochepa amakhala ndi kuwala kochepa, zomwe zimapangitsa kuti asawoneke bwino. Kuphatikiza apo, malingaliro a chiphunzitso cha ray sangakhale olondola kwenikweni pa kusiyana kwakukulu kapena ma frequency ena. Phokoso, zolakwika zosankhidwa, ndi kusatsimikizika kwa malo a hypocenter zingakhudzenso zotsatira za inversion. Chifukwa chake, kuwunika kwa resolution ndi kuphatikiza njira zambiri ndikofunikira kuti tipewe kutanthauzira mopitirira muyeso.
Kutseka
Kujambula kwa zivomerezi ndi chida chofunikira kwambiri pofufuza kapangidwe ka mkati mwa Dziko Lapansi kuyambira pamlingo wapafupi mpaka padziko lonse lapansi. Maziko ake a chiphunzitso amadalira ubale womwe ulipo pakati pa zinthu zotanuka pa miyala ndi kufalikira kwa mafunde, komanso kuthetsa mavuto otsutsana omwe amafunikira kukhazikika ndi kuyesa kwa mayankho. Ntchito zake ndi zazikulu: kuyambira kupanga ma mapping subducting slabs ndi magma a volcano mpaka kufufuza mphamvu ndi kuwunika zoopsa za chivomerezi. Ndi kupita patsogolo kwa maukonde a zivomerezi, makompyuta, ndi njira zosinthira (kuphatikiza kutembenuza kwathunthu kwa mafunde), kujambula kwa zivomerezi kukutha kupanga zithunzi zakuthwa komanso zophunzitsa zambiri pazolinga zasayansi komanso zochepetsera masoka.
Ngati mukufuna, nditha kusintha nkhaniyi kukhala yophunzirira bwino (yokhala ndi mawu ndi zolemba), kapena kuyang'ana kwambiri pa imodzi mwa ntchito (monga tomography ya mapiri ophulika kapena mphamvu ya geothermal).
