Ke Kumu Manaʻo a me ka Hoʻohana ʻana o ke ʻAno VLF ma Geophysics
Pendahuluan
ʻO ke ʻano hana VLF (Very Low Frequency) he ʻano hana geophysical electromagnetic e hoʻohana ana i nā nalu lekiō alapine haʻahaʻa loa (ma kahi o 15-30 kHz) e ʻike i nā ʻano like ʻole o nā waiwai uila ma lalo o ka ʻilikai. ʻAʻole e like me ke ʻano hana geoelectric resistivity e koi ana i ka hoʻokomo ʻana o ke au ma o nā electrodes i loko o ka lepo, ʻo ke ʻano hana VLF he passive maʻamau no ka mea hoʻohana ia i nā kumu nalu mai nā mea hoʻoili lekiō VLF i loaʻa koke (maʻamau no nā kamaʻilio koa a i ʻole ka hoʻokele). Me kēia ʻano, ʻo VLF kahi ʻano hana kūpono, wikiwiki, a ʻoi aku ka maʻalahi no nā ana mua o nā pahuhopu geological like ʻole, ʻoi aku hoʻi nā ʻano hana conductive e like me nā ʻāpana hewa, nā haki i piha i ka wai, ka mineralization sulfide, a me nā ala wai honua.
Kūkākūkā kēia ʻatikala i ke kumu kumumanaʻo o ke ʻano VLF, nā loina ana, nā ʻano wehewehe, a me nā noi maʻamau ma ke kahua o ka ʻimi ʻana a me ka geophysics kaiapuni.
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Kumu Manaʻo o ke ʻAno VLF
1. Ke kumumanaʻo o nā nalu electromagnetic a me ka induction
ʻO nā hōʻailona VLF he mau nalu electromagnetic i haku ʻia me nā ʻāpana kahua uila (E) a me magnetic (H) e pālahalaha ana ma o ka lewa a launa pū me ka ʻili o ka Honua. Ke pā kēia mau nalu i ka Honua, pālahalaha kekahi o ka ikehu ma ke ʻano he mau nalu ʻili a komo kekahi i loko o ka ʻili honua. Inā ʻoi aku ka kiʻekiʻe o ka conductivity uila o kahi mea a i ʻole kahi ma mua o ka pōhaku e hoʻopuni ana (e.g., ka lepo pulu, nā wahi hewa wai, nā aa sulfide), e hoʻoulu ke kahua electromagnetic mua i nā kahe eddy i loko o ke kino conductive.
Hoʻopuka kēia mau au eddy i nā kahua lua, a laila ʻike ʻia e ka mea kani. I nā huaʻōlelo ʻē aʻe, kū mai nā anomalies VLF ma muli o ka ʻokoʻa o ka pane ma waena o ke kahua mua mai ka mea hoʻoili a me ke kahua lua i hoʻokomo ʻia i loko o ka ʻōnaehana subsurface.
2. Kumu kahua mua: mea hoʻoili VLF
Hoʻohana ke ʻano hana VLF i nā mea hoʻoili VLF mana kiʻekiʻe e hoʻoili i kahi hōʻailona paʻa ma kahi alapine kikoʻī. Ma nā wahi he nui, hiki ke loaʻa i nā kikowaena VLF he nui i ka manawa like, akā koho pinepine nā mea hoʻohana i nā mea hoʻoili e:
- ʻoi aku ka ikaika o ka hōʻailona a paʻa loa ma kahi o ke ana ʻana,
- ua lawa ka kuhikuhi o ka mea hoʻoili e kūlike me ke kuhikuhi o ka pahuhopu (no ka laʻana, kū pololei i ke kuhikuhi o ka hewa e ʻimi ʻia nei),
– ua kūpono ke alapine (frequency) a me nā kūlana hoʻolaha.
Ma muli o ka hoʻohana ʻana i kahi kumu o waho, ʻaʻole pono kēia ʻano hana i kahi mīkini hana a i ʻole kahi mea hoʻoili loop ma ke kula, e hoʻolilo ana i ka anamanaʻo i mea kūpono loa.
3. Nā palena koʻikoʻi: conductivity a me ka hohonu o ke komo ʻana
Hoʻopilikia nui ʻia ka pane VLF e ka conductivity uila (σ) o ka medium. ʻO kahi manaʻo i hoʻohana pinepine ʻia e kuhi i ka mamao e hiki ai i kahi nalu ke "komo" ʻo ia ka hohonu o ka ʻili (δ), ʻo ia ka hohonu e hāʻule ai ka amplitude o ke kahua i kahi o 1/e o kona waiwai ʻili. I ka ʻōlelo maʻalahi:
– Hoʻonui ka penetration ke kiʻekiʻe ka resistivity (haʻahaʻa ka conductivity).
– E emi ana ka penetration ke kiʻekiʻe ka conductivity, no ka mea, ua hoʻomaʻū koke ʻia ke kahua.
Me nā alapine (~kHz), ʻike nui ʻia kēia ʻano hana i nā hohonu pāpaʻu a waena (nā ʻumi mika, ʻoi aku paha ma muli o nā kūlana geological). No laila, kūpono loa ʻo VLF no ke kaha kiʻi ʻana i nā hale pāpaʻu e like me nā ʻāpana haki a me nā hewa.
4. Nā ʻāpana kahua a me ka polarization
Ma ka hana VLF, ʻo ke ana mua ʻana ka loli o ke kahua magnetic (a i ʻole ke kahua hiolo) e like me ka mea i hoʻopili ʻia e ke ʻano alakaʻi. Ke hoʻopilikia ke kahua mua i kahi alakaʻi elongated (e.g., kahi ʻāpana hewa), hoʻokumu ʻia kahi kahua lua me nā ʻāpana e hoʻoulu ai i nā loli i:
- ke kihi hiō (ke kihi hiō o ka ʻāina),
– nā ʻāpana in-phase (maoli) a me quadrature (hoʻokalakupua) o ka hōʻailona.
Pili ka ʻāpana in-phase i kahi pane alakaʻi "maikaʻi" a pololei hoʻi, ʻoiai ʻo ka quadrature e pili pinepine ana i nā hopena phase a me nā waiwai alakaʻi/lepo a me nā kūlana geometry a me ka hohonu.
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Nā Kumumanaʻo Ana o ke Kahua
1. Nā kaʻina hana noiʻi
Hana ʻia nā ana VLF ma ka hele wāwae ʻana ma ke ala ana (profile) ma nā wahi kikoʻī (e.g., 5-20 m). Kuhikuhi ka mea hoʻohana i ka mea kani i kahi mea hoʻoili i koho ʻia a laila hoʻopaʻa i nā palena VLF ma kēlā me kēia kikowaena. Hana pinepine nā mea hoʻomaʻamaʻa i nā hala like ʻole e hana i kahi palapala ʻāina anomaly ʻelua-dimensional.
ʻO ke kī i ke geometry ma VLF: ʻike ʻia nā anomalies maopopo loa ke hui maikaʻi ke ala a me ke kuhikuhi o ka pahuhopu i ke kuhikuhi kahua mua. ʻO nā pahuhopu alakaʻi elongated i kuhikuhi kokoke i ka transmitter e hana pinepine i nā pane nāwaliwali.
2. ʻIkepili nui: in-phase a me quadrature
Hoʻopuka pinepine nā mea kani VLF hou i ʻelua mau kahawai nui:
– I loko o ka pae (% a i ʻole nā kekelē): pane i ka pae me ke kahua mua.
– Quadrature (% a i ʻole kekelē): pane ʻokoʻa pae 90°.
He mea nui kēia mau ala ʻelua no ka mea:
– ʻIke pinepine ʻia ka in-phase no nā alakaʻi maikaʻi a pāpaʻu hoʻi.
- Hoʻonui pinepine ka Quadrature i nā alakaʻi nāwaliwali, nā alakaʻi hohonu, a i ʻole i loko o nā pāpaho e hoʻoulu ai i nā hopena dispersion/phase lag.
3. Hoʻoponopono ʻikepili: Fraser a me Karous-Hjelt kānana
He paʻakikī pinepine ka heluhelu ʻana i ka ʻikepili VLF maka ma muli o kona mau loli liʻiliʻi i hoʻoulu ʻia e ka walaʻau. ʻElua mau ʻano hana hana kaulana:
– Kānana Fraser
Ke hoʻololi nei i ka ʻikepili in-phase i kahi ʻano maʻalahi e wehewehe ʻia ma ka hōʻike ʻana i nā loli gradient. ʻO ka hopena he piʻo pinepine me nā piko e pili ana i nā kūlana alakaʻi.
– Kānana Karous–Hjelt
Hoʻopuka i kahi pseudo-section density o kēia manawa e nānā i ka wahi pili a me ka hohonu o nā alakaʻi. ʻOiai ʻaʻole ia he inversion "ʻoiaʻiʻo" e like me ka ERT a i ʻole EM hou, hoʻomaʻamaʻa kēia kānana i ka wehewehe wikiwiki, ʻoi aku hoʻi no nā ʻano linear.
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Ka Wehewehe ʻana i ka Anomaly VLF
1. Nā ʻano laulā o nā anomalies alakaʻi
ʻO nā alakaʻi linear e like me nā ʻāpana hewa e hāʻawi pinepine i nā ʻano maʻamau:
- ka hoʻololi ʻana o ka hōʻailona (zero crossing) i loko o ka pae,
- nā piko/concavities symmetrical a asymmetrical paha ma muli o ka pali a me ka hohonu,
- ka pane quadrature e kōkua ana e hoʻoholo inā paha ma muli o kahi alakaʻi maoli a i ʻole kahi hopena topographic/heterogeneity superficial wale nō ka anomaly.
ʻO ka maʻamau, hōʻike nā ʻano ʻē ikaika:
- ke alakaʻi kiʻekiʻe (e.g. ka mineralization sulfide a i ʻole ka pālolo pulu),
- alakaʻi pāpaʻu,
– ke kuhikuhi “kūpono” o ke alakaʻi e pili ana i ke kuhikuhi o ka mea hoʻoili.
2. Ka maopopo ʻole a me nā palena
He mau palena ko ke ʻano VLF e pono e hoʻomaopopo ʻia:
– Hilinaʻi ka mea hoʻoili: hilinaʻi ka maikaʻi o ka ʻikepili i ka ikaika o ka hōʻailona a me ka hoʻopilikia ʻana o ka hoʻolaha ʻana.
– Pilikia i ka walaʻau moʻomeheu: hiki i nā laina mana, nā pā uea, nā paipu, nā alahao, a me nā ʻoihana ʻē aʻe ke hana i nā ʻano ʻē wahaheʻe.
– Ka wehewehe ʻana kū hoʻokahi ʻole: hiki ke hana ʻia nā ʻano ʻē e nā hui like ʻole o ka hohonu, ka pali, a me ka conductivity.
– Ka hohonu palena: kūpono ma ke ʻano laulā no nā pahuhopu pāpaʻu-waena; no nā pahuhopu hohonu, pono nā ʻano EM ʻē aʻe a i ʻole geoelectric.
No laila, kūpono ʻo VLF ma ke ʻano he ʻano ʻike mua a i ʻole ke ʻano palapala ʻāina e hōʻoia ʻia e nā ʻano hana ʻē aʻe e like me ke kū'ē ʻana o 2D/ERT, IP, magnetic, a i ʻole ka wili ʻana.
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Ka Hoʻohana ʻana o ke ʻAno VLF ma Geophysics
1. Ka palapala ʻāina ʻana o nā ʻāpana hewa a me nā haki
ʻO ka hoʻohana maʻamau o VLF ka ʻike ʻana i nā ʻāpana kūkulu i alakaʻi ʻia ma muli o ka wai, ka lepo, a i ʻole ka hoʻololi ʻana. I ka ʻimi ʻana i ka geothermal, no ka laʻana, hana nā hewa a me nā haki ma ke ʻano he mau ala wai; Kōkua ʻo VLF i ka palapala wikiwiki ʻana i kēia mau ala ma ka ʻili.
2. Ka ʻimi ʻana i ka wai honua
Ma ka hydrogeophysics, hoʻohana ʻia ʻo VLF e ʻike ai:
– nā haki ma ka pōhaku paʻakikī (aquifer pōhaku paʻakikī),
- nā pilina lithologic e hoʻopaʻa ana i ka wai,
– ka ʻāpana i hoʻomāʻū ʻia i ka wai a ʻoi aku ka hoʻoili ʻana o ka uila.
Hoʻohana pinepine ʻia kēia ʻano hana e hoʻoholo ai i nā wahi e hiki ai ke ʻeli luawai, ʻoi aku hoʻi ma nā wahi pōhaku metamorphic a i ʻole igneous.
3. Ka ʻimi ʻana i nā minerala
Hiki iā VLF ke ʻike i ka mineralization conductive e like me nā sulfides nui, graphite, a i ʻole kekahi mau wahi hoʻololi. ʻOiai ʻaʻole ia ke ʻano mua no ka loiloi mālama, he kūpono ka VLF no:
- ke kaha ʻana i nā aʻa conductive,
- ka palapala ʻāina o nā ʻano hana e kāohi ana i ka mineralization,
- ka nānā wikiwiki ʻana i nā wahi nui e hoʻoholo ai i nā pahuhopu holomua.
4. Geophysics kaiapuni a me ka ʻenekinia
Ma nā haʻawina kaiapuni, kōkua ʻo VLF i ka ʻike ʻana:
- ke ala e kahe ai ke koko ma nā pā wai/nā ʻauwaha,
- nā wahi lepo i piha i ka wai e maʻalahi i ka ʻāina hāʻule,
– hōʻailona o ka haumia o nā plume inā ʻokoʻa ke alakaʻi ʻana.
Hiki ke hoʻohana ʻia ʻo VLF i nā pae mua o nā noiʻi geotechnical ma ke ʻano he mea hoʻohālike wikiwiki o nā heterogeneities conductive kokoke i ka ʻili.
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Ka hopena
ʻO ke ʻano hana VLF kahi ʻenehana electromagnetic passive e hoʻohana ana i nā mea hoʻoili alapine haʻahaʻa loa e ʻike i nā ʻano hana o lalo o ka honua. Aia kona kumu kumumanaʻo ma ka induction electromagnetic: hoʻoulu kahi kahua mua i kahi au i loko o kahi alakaʻi, e hana ana i kahi kahua lua i ana ʻia ma ke ʻano he loli i ka pae a me ka quadrature. Me kāna ana wikiwiki ʻana i ke kahua, ke kumukūʻai haʻahaʻa, a me ka hiki ke hōʻike i nā ʻano linear e like me nā hewa a me nā haki, he mea pono loa ʻo VLF no ka ʻimi ʻana i ka wai honua, ka palapala ʻāina ʻano geological, ka nānā ʻana i nā minerala, a me nā noi kaiapuni. Eia nō naʻe, he maopopo ʻole kona wehewehe ʻana a he koʻikoʻi i ka walaʻau moʻomeheu, no laila pono e hui pū ʻia nā hopena VLF me nā ʻano hana geophysical ʻē aʻe no ka hōʻoia.
Inā makemake ʻoe, hiki iaʻu ke hoʻohui i kahi ʻāpana laʻana o ke kahe anamanaʻo VLF mai ka hoʻolālā ʻana i ka palapala ʻāina anomaly, a i ʻole e hana i kahi ʻano ʻatikala ʻepekema piha me nā kuhikuhi maʻamau.
