Maziko a Chiphunzitso ndi Kugwiritsa Ntchito Njira ya VLF mu Geophysics
Pendauluan
Njira ya VLF (Very Low Frequency) ndi njira ya electromagnetic geophysical yomwe imagwiritsa ntchito mafunde a wailesi otsika kwambiri (pafupifupi 15–30 kHz) kuti izindikire kusiyana kwa mphamvu zamagetsi za pansi pa nthaka. Mosiyana ndi njira ya geoelectric yotsutsa yomwe imafuna kulowetsedwa kwamagetsi kudzera mu ma electrodes pansi, njira ya VLF nthawi zambiri imakhala yopanda ntchito chifukwa imagwiritsa ntchito magwero a mafunde kuchokera ku ma transmitter a wailesi a VLF omwe amapezeka mosavuta (nthawi zambiri polankhulana ndi asilikali kapena kuyenda). Ndi khalidwe ili, VLF ndi njira yothandiza, yachangu, komanso yotsika mtengo yofufuzira koyamba zolinga zosiyanasiyana za geological, makamaka zomangamanga zoyendetsera magetsi monga malo olakwika, kusweka kwa madzi, sulfide mineralization, ndi njira za geological. madzi apansi panthaka.
Nkhaniyi ikufotokoza za maziko a chiphunzitso cha njira ya VLF, mfundo zoyezera, njira zotanthauzira, ndi ntchito zambiri m'munda wa kufufuza ndi geophysics ya zachilengedwe.
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Maziko a Chiphunzitso cha Njira ya VLF
1. Lingaliro la mafunde amagetsi ndi kulowetsa
Zizindikiro za VLF ndi mafunde amagetsi okhala ndi zigawo zamagetsi (E) ndi maginito (H) zomwe zimafalikira mumlengalenga ndikugwirizana ndi pamwamba pa Dziko Lapansi. Mafunde awa akagunda Dziko Lapansi, mphamvu zina zimafalikira ngati mafunde apamwamba ndipo zina zimalowa pansi pa nthaka. Ngati chinthu kapena dera lili ndi mphamvu zamagetsi zambiri kuposa miyala yozungulira (monga dongo lonyowa, malo amadzi olakwika, mitsempha ya sulfide), gawo loyambirira lamagetsi limayambitsa mafunde a eddy mkati mwa thupi loyendetsa.
Mafunde a eddy awa amapanga minda yachiwiri, yomwe kenako imagwidwa ndi chipangizocho. Mwa kuyankhula kwina, zolakwika za VLF zimachitika chifukwa cha kusiyana kwa mayankho pakati pa munda woyamba kuchokera ku chotumizira ndi munda wachiwiri womwe umachitika pansi pa nthaka.
2. Gwero lalikulu la munda: Chotumiza cha VLF
Njira ya VLF imagwiritsa ntchito ma transmitter a VLF amphamvu kwambiri omwe amatumiza chizindikiro chokhazikika pa frequency inayake. M'madera ambiri, malo angapo a VLF amatha kulandiridwa nthawi imodzi, koma ogwiritsa ntchito nthawi zambiri amasankha ma transmitter omwe:
- chizindikirocho chimakhala champhamvu kwambiri komanso chokhazikika pamalo ofufuzira,
- njira yotumizira ikugwirizana mokwanira ndi komwe cholinga chake chili (mwachitsanzo, molunjika komwe cholakwika chikufufuzidwa),
- kuchuluka kwa nthawi ndi momwe zimafalitsira n'kokwanira.
Chifukwa chakuti imagwiritsa ntchito gwero lakunja, njira iyi siifuna jenereta kapena chotumizira cha loop m'munda, zomwe zimapangitsa kuti kafukufukuyo agwire bwino ntchito.
3. Zofunikira pa magawo: kuyendetsa bwino mphamvu ndi kuzama kwa kulowa
Kuyankha kwa VLF kumakhudzidwa kwambiri ndi mphamvu yamagetsi (σ) ya chinthucho. Lingaliro lomwe nthawi zambiri limagwiritsidwa ntchito poyesa kutalika komwe mafunde "angalowe" ndi kuya kwa khungu (δ), komwe ndi kuzama komwe kutalika kwa malo kumatsika kufika pafupifupi 1/e ya mtengo wake wa pamwamba. Mwachidule:
– Kulowa kumawonjezeka pamene resistivity ili pamwamba (conductivity ndi yochepa).
– Kulowa kwa madzi kumachepa pamene mphamvu ya mpweya imakhala yokwera, chifukwa malo ozungulira mpweya amanyowa mofulumira.
Ndi ma frequency a VLF (~kHz), njira iyi nthawi zambiri imakhala yogwirizana ndi kuya kosaya kwambiri mpaka kwapakati (makumi a mamita, mwina kutengera momwe zinthu zilili). Chifukwa chake, VLF ndi yoyenera kwambiri pojambula mapangidwe osaya kwambiri monga madera osweka ndi zolakwika.
4. Zigawo za m'munda ndi kugawanika kwa magawo
Mu machitidwe a VLF, muyeso woyamba ndi kusintha kwa mphamvu ya maginito (kapena kupendekeka kwa munda) monga momwe zimakhudzidwira ndi kapangidwe ka conductive. Pamene mphamvu yoyamba ikukhudza kondakitala wautali (monga malo olakwika), mphamvu yachiwiri imapangidwa ndi zigawo zomwe zimayambitsa kusintha kwa:
- ngodya yopendekera (ngodya yopendekera ya malo),
- zigawo za chizindikiro zomwe zili mu gawo (zenizeni) ndi quadrature (zongopeka).
Gawo la mkati mwa gawo limakhudzana ndi yankho la kondakitala "labwino" komanso lolunjika, pomwe quadrature nthawi zambiri imakhudzana ndi zotsatira za gawo ndi mawonekedwe a kondakitala/dongo komanso mawonekedwe ndi kuya kwa zinthu.
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Mfundo Zoyezera Munda
1. Njira zofufuzira
Kafukufuku wa VLF amachitika poyenda m'njira yoyezera (mbiri) pamalo enaake (monga, mamita 5–20). Wogwiritsa ntchito amaloza chidacho ku chotumizira chosankhidwa kenako n’kulemba magawo a VLF pa siteshoni iliyonse. Akatswiri nthawi zambiri amapanga ma pass angapo ofanana kuti apange mapu osazolowereka a mbali ziwiri.
Chinsinsi cha geometry mu VLF ndi: zolakwika zoonekeratu kwambiri zimawonekera pamene njira ndi momwe chandamale chimayendera bwino mbali yoyambira ya munda. Zolinga zoyendetsera mpweya zomwe zimayendetsedwa mozungulira pafupi ndi chotumizira nthawi zambiri zimabweretsa mayankho ofooka.
2. Deta yaikulu: mu gawo ndi quadrature
Zipangizo zamakono za VLF nthawi zambiri zimapanga njira ziwiri zazikulu:
– Mu gawo (% kapena madigiri): yankho mu gawo ndi gawo loyambirira.
– Quadrature (% kapena madigiri): Yankho la kusiyana kwa gawo la 90°.
Njira ziwirizi ndizofunikira chifukwa:
- Nthawi zambiri mkati mwa gawoli mumapezeka ma conductor abwino komanso osaya kwambiri.
- Quadrature imakonda kuwonjezeka kwa ma conductor ofooka, ma conductor akuya, kapena m'malo olumikizirana omwe amachititsa zotsatira za dispersion/phase lag.
3. Kukonza deta: Zosefera za Fraser ndi Karous-Hjelt
Deta ya VLF yosaphika nthawi zambiri imakhala yovuta kuiwerenga chifukwa cha kusintha kwake kochepa komwe kumachitika chifukwa cha phokoso. Njira ziwiri zodziwika bwino zogwiritsira ntchito ndi izi:
- Fyuluta ya Fraser
Kusintha deta yomwe ili mu gawo kukhala mawonekedwe osavuta kutanthauzira powunikira kusintha kwa ma gradient. Zotsatira zake nthawi zambiri zimakhala zokhota zokhala ndi ma peak ofanana ndi malo a kondakitala.
- Karous–Hjelt Fyuluta
Imapanga gawo la pseudo-section la kuchulukana kwa magetsi kuti liwonetse malo ndi kuzama kwa ma conductor. Ngakhale kuti si "chowonadi" monga ERT kapena EM yamakono, fyuluta iyi imathandiza kutanthauzira mwachangu, makamaka pa kapangidwe ka mzere.
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Kutanthauzira kwa VLF Anomaly
1. Makhalidwe ambiri a zolakwika za kondakitala
Ma conductor a mzere monga malo olakwika nthawi zambiri amayambitsa njira zotsatirazi:
- kusintha kwa chizindikiro (zero crossing) mu gawo,
- nsonga/mikwingwirima yofanana kapena yosagwirizana kutengera kutsetsereka ndi kuya,
- yankho la quadrature lomwe limathandiza kudziwa ngati vutolo likuchitika chifukwa cha kondakitala weniweni kapena chifukwa cha topographic/heterogeneity chabe.
Zovuta zazikulu nthawi zambiri zimasonyeza:
- mphamvu yochuluka yoyendetsera mpweya (monga sulfide mineralization kapena dongo lonyowa),
- kondakitala wosaya kwambiri,
- Kuyang'ana kwa "kondakitala" koyenera poyerekeza ndi komwe chotumizira chimalowera.
2. Kusamveka bwino ndi zoletsa
Njira ya VLF ili ndi zofooka zomwe ziyenera kumvedwa:
- Kudalira kwa transmitter: ubwino wa deta umadalira mphamvu ya chizindikiro ndi kusokoneza kwa kufalikira.
- Yosakhudzidwa ndi phokoso la chikhalidwe: zingwe zamagetsi, mipanda ya waya, mapaipi, njanji, ndi zomangamanga zina zingayambitse zolakwika zabodza.
- Kutanthauzira kosakhala kwapadera: zolakwika zimatha kuchitika chifukwa cha kuphatikiza kosiyanasiyana kwa kuya, kutsetsereka, ndi kuyendetsa mphamvu.
- Kuzama kochepa: nthawi zambiri kumagwira ntchito bwino pa malo osaya kwambiri mpaka apakati; pa malo ozama kwambiri njira zina za EM kapena geoelectric zimafunika.
Chifukwa chake, VLF ndi njira yabwino kwambiri yodziwira kapena kupanga mapu yomwe imatsimikiziridwa ndi njira zina monga 2D resistivity/ERT, IP, magnetic, kapena drilling.
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Kugwiritsa Ntchito Njira ya VLF mu Geophysics
1. Kujambula mapu a malo olakwika ndi osweka
Kugwiritsa ntchito kwambiri kwa VLF ndiko kuzindikira madera omwe ali ndi mphamvu yoyendetsera zinthu chifukwa cha madzi, dongo, kapena kusintha kwa nthaka. Mwachitsanzo, pofufuza za kutentha kwa dziko lapansi, zolakwika ndi kusweka kwa nthaka zimakhala ngati njira zamadzimadzi; VLF imathandiza kupanga mapu a njirazi mofulumira pamwamba.
2. Kufufuza madzi apansi pa nthaka
Mu hydrogeophysics, VLF imagwiritsidwa ntchito kupeza:
- kusweka kwa miyala yolimba (aquifer ya miyala yolimba),
- kulumikizana kwa lithologic komwe kumakola madzi,
- malo owonongeka omwe ali ndi madzi ambiri komanso oyenda bwino.
Njira imeneyi nthawi zambiri imagwiritsidwa ntchito podziwa malo omwe angakumbe zitsime, makamaka m'malo omwe miyala yasintha kapena ya igneous imagwera.
3. Kufufuza za mchere
VLF imatha kuzindikira mchere woyendetsedwa ndi ma ducts monga ma sulfide akuluakulu, graphite, kapena malo ena osinthira. Ngakhale kuti si njira yayikulu yowunikira malo osungira, VLF imagwira ntchito pa:
- kutsatira mitsempha yoyendetsa magazi,
- kujambula njira zomwe zimawongolera kuchuluka kwa mchere m'nthaka,
- kufufuza mwachangu madera akuluakulu kuti mudziwe zolinga zapamwamba.
4. Geophysics ya zachilengedwe ndi uinjiniya
Mu maphunziro okhudza chilengedwe, VLF imathandiza kuzindikira:
- njira yotuluka madzi pamadamu/makhoma,
- malo okhala ndi nthaka yodzaza ndi madzi omwe nthawi zambiri amagwa pansi,
- chizindikiro cha kuipitsidwa kwa nthunzi ngati mphamvu ya mpweya ikusiyana.
VLF ingagwiritsidwenso ntchito kumayambiriro kwa kafukufuku wa geotechnical ngati chida chofufuzira mwachangu cha kusiyana kwa ma conductive conductive pafupi ndi pamwamba.
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Mapeto
Njira ya VLF ndi njira yamagetsi yopanda mphamvu yomwe imagwiritsa ntchito ma transmitter otsika kwambiri kuti izindikire kapangidwe kake ka pansi pa nthaka. Maziko ake a chiphunzitso amadalira kulowetsedwa kwa magetsi: gawo loyamba limayambitsa mphamvu mu kondakitala, zomwe zimapangitsa gawo lachiwiri lomwe limayesedwa ngati kusintha kwa gawo ndi quadrature. Ndi kufufuza kwake mwachangu kwa gawo, mtengo wotsika, komanso kuthekera kowonetsa kapangidwe ka mzere monga zolakwika ndi kusweka, VLF ndi yothandiza kwambiri pa kufufuza madzi apansi panthaka, mapu a kapangidwe ka nthaka, kufufuza miyala, ndi kugwiritsa ntchito zachilengedwe. Komabe, kutanthauzira kwake n'kosavuta komanso kogwirizana ndi phokoso la chikhalidwe, kotero zotsatira za VLF ziyenera kuphatikizidwa ndi njira zina za nthaka kuti zitsimikizire.
Ngati mukufuna, nditha kuwonjezera gawo la chitsanzo cha kayendedwe ka kafukufuku wa VLF kuyambira kukonzekera mpaka mapu osazolowereka, kapena kupanga kapangidwe kathunthu ka nkhani zasayansi ndi mawu wamba.
