Te Tātaritanga Maha-Wāhanga i roto i te Tūhuratanga Rūwhenua
Kua roa te mōhio whānuitia o te ru whenua tūhura hei tikanga matua mō te mahere i ngā hanganga o raro i te mata, inā koa i roto i ngā umanga hinu me te hau, te waiariki, me te hangarau matawhenua. I ngā wā o mua, ka tuhia ngā raraunga ru whenua hei ngaru pēhi, hei ngaru-P rānei. Heoi, nā te whanaketanga o te hangarau hopu me te hiahia mō te whakamārama taipitopito ake kua akiaki i te whakamahinga o ngā raraunga ru whenua maha-wāhanga—arā, te tuhi i te neke atu i te kotahi wāhanga o te nekehanga whenua—hei hopu i tētahi urupare o raro i te mata he nui ake. He huarahi nui te tātari maha-wāhanga inaianei mō te mārama ki te lithology, ngā wai pore, te anisotropy, tae atu ki ngā āhuatanga pakaru, he uaua katoa te hopu me ngā raraunga ru whenua kotahi-wāhanga.
Ngā Ariā Taketake o te Ruānuku Maha-Wāhanga
Ko te kupu "maha-wāhanga" e pā ana ki te hopu i te nekehanga o ngā matūriki i ngā taha maha. I roto i ngā rangahau whenua, ka hopukina e ngā geophone 3-wāhanga (3C) te nekehanga i te taha poutū (Z) me ngā taha whakapae e rua (X me Y). I te moana, ka mahia te hopu i ngā maha-wāhanga mā te whakamahi i ngā pūoko taura raro-moana (OBN/OBS) e ine ana i te pēhanga (hydrophone) me te tere o ngā matūriki (geophone), e whakarato ana i ngā mōhiohio tāpiri mō te tukatuka me te whakamaori.
Ko ngā ngaru ru whenua tino nui i tēnei horopaki ko ngā ngaru-P me ngā ngaru-S. Ka horapa ngā ngaru-P mā te pēhi me te whakawhānui i te reo, ko ngā ngaru-S ia ka kutikuti. E rua ngā momo pōraritanga o ngā ngaru-S (SV me SH) ā, he tino tairongo ā rāua urupare ki te anisotropy me te pakaru. Nā te āhua ā-tinana, kāore e taea e ngā ngaru-S te horapa mā roto i ngā wai parakore, nō reira he pai ake te whakaatu a tā rātou urupare i te anga toka i te wai pūwero. Ko tēnei rerekētanga o te tairongo te mea e ātaahua ai te tātari maha-wāhanga: mā te whakakotahitanga o ngā mōhiohio P me S ka whakapai ake i te kaha ki te wehewehe i ngā āhuatanga toka.
Ngā Momo Raraunga i roto i te Ruānuku Maha-Wāhanga
I roto i ngā mahi tūhuratanga, ko ētahi momo raraunga maha-wāhanga e tātarihia pinepinetia ana ko:
1. PP (P-ki-P): Ka whakaatahia, ka tuhia hoki ngā ngaru-P hei P, he rite ki te ru whenua tuku iho.
2. PS (P-ki-S): Ngā ngaru-P, ina whakaatahia/hurihia, ka huri hei ngaru-S, ā, ka tuhia ki te wāhanga whakapae. E kiia ana ngā raraunga PS he ngaru-hurihia he ru whenua.
3. SS (S-ki-S): Ka whakaatahia ngā ngaru-S hei S, me te hiahia i tētahi pūtake ngaru-S (he mea noa ake i runga i te whenua me ngā rangahau motuhake).
4. Ngā momo ngaru mata me ngā momo ngaru ahunga: Pērā i a Love/Rayleigh, e kiia ana he haruru i ētahi wā engari ka taea hoki te whakamahi mō te whakaahuatanga papaku.
He tino whai hua ngā raraunga PS nā te mea ka taea te tiki mai mā te whakamahi i ngā pūtake P noa (pēnei i ngā vibroseis, i ngā pū hau rānei), engari mā ngā kaiwhiwhi 3C ka taea te hopu i ngā wāhanga S kua tahurihia.
Te Hokonga: Ngā Wero me ngā Kī ki te Angitu
Ko te angitu o te tātaritanga maha-wāhanga e whakawhirinaki nui ana ki te kounga o te hopunga. I runga i te whenua, he mea nui te whakatakotoranga whakapae o te pūoko: ka taea e ngā hapa azimuth geophone te huna i te polarization o te ngaru-S me te whakauaua i te tātaritanga anisotropy. Ko te hononga pūoko ki te whenua, ngā āhuatanga tata-mata uaua, me ngā rerekētanga pumau he wero anō.
I te moana, ko te painga o te whakamahinga o te OBS/OBN he kaha ki te hopu i tētahi mara ngaru tino whānui ake, engari ka nui ake te uaua o te tukatuka: me aromatawai te whakatakotoranga o te pūoko i runga i te papa moana, me whakatika ngā pānga o te iahiko/tītaha, ā, me whai mahi motuhake te wehenga o ngā ngaru P me te S pērā i te wehenga mara ngaru.
Hei tāpiritanga, ko ngā hoahoa rangahau maha-wāhanga e whakaaro ana ki te kapinga azimuth pai ake, nā te mea ka tino āwhinahia te tātari anisotropy (hei tauira, te anisotropy i puta mai i te whati) e ngā rerekētanga azimuth.
Tukatuka Raraunga Maha-wāhanga
Ehara i te mea ko te tukatuka maha-wāhanga he tāpiri noa i ngā hongere raraunga. Me whai whakaaro ia taahiraa tukatuka ki ngā rerekētanga o te ahupūngao o te horapa P me te S. Ko ētahi o ngā taahiraa matua ko:
1. Te Hurihanga o te Wāhanga me te Whakatikatika i te Aronga
I roto i ngā raraunga 3C, me huri ngā wāhanga whakapae (X, Y) ki roto i tētahi pūnaha taunga radial-transverse e pā ana ki te ahunga pūtake-kaiwhiwhi. Mā tēnei hurihanga ka wehea te pūngao SV me te SH, inā koa i roto i ngā raraunga PS. I roto i te moana, kāore i te tino mōhiotia te whakatakotoranga o ngā geophone o te papa moana, nō reira me whakatau tata mai i te tohu (hei tauira, mā te whakamahi i te ahunga matua o te polarization o te ngaru-P).
2. Te Wehenga o te Mara Ngaru
Ko te whāinga o tēnei taahiraa he wehewehe i te pūngao o runga me te pūngao o raro, me te wehewehe i ngā wāhanga P me te S i ngā wā katoa e taea ai. I roto i te OBC/OBS, mā te whakakotahitanga o ngā hydrophone me ngā geophone ka taea te wehewehe i ngā ngaru o runga me raro, ka whakaiti i ngā maha me te whakapai ake i te kounga o te ahua.
3. Whakatikatika Tūmau me te Tata-Mata
He maha ngā wā ka puta he whakapōturitanga nui i roto i ngā ngaru-S nā te tere iti me te aro nui ake ki ngā rerekētanga papaku. Kāore te S tūmau e rite tonu ki te P tūmau, nō reira me whai rautaki motuhake te tukatuka PS, pērā i te whakatau tata tūmau i te wā taenga mai o ngā ngaru S kua hurihia, i te huarahi hurihanga tata rānei.
4. Te Tātari Tere me te Nekehanga
He iti ake te tere S i te P, nō reira he roa ake te wā haere PS. He kore taurite te nekehanga i roto i te PS nā te mea he rerekē ngā ara P me te S. He mea nui te whiriwhiri i te tauira tere mō te whakaahua PS (hei tauira, VPS, te ōwehenga Vp/Vs rānei) hei ārai i te tūnga hē o te whakaata.
5. Te Hekenga PS me te Rēhitatanga Takahanga
Ko te nekehanga mō te PS ka mahia mā te whakamahi i te huarahi nekehanga ngaru-hurihuri mā te whakamahi i ngā tauira Vp me Vs. He maha ngā wā ka mahia te rēhitatanga takahanga i muri mai hei whakarite i ngā whakaata PP me PS ki te pae kotahi. He mea nui tēnei whakaritenga mō te tātari āhuatanga honohono me te hurihanga.
6. Te Tukatuka Anisotropy me te Wehewehenga Ngaru-Kutikuti
I roto i ngā pāpāho anisotropic, ka taea e ngā ngaru-S te wehewehe kia rua ngā ngaru orthogonal me ngā tere rerekē (te wehewehenga ngaru-kutikuti). Ka taea te whakamahi i te tātari wehewehe hei whakatau tata i te aronga pakaru matua me te nui o te anisotropy. He tino whai hua tēnei i roto i ngā puna waro pakaru, i ngā kirikiri anisotropic rānei.
Te Whakamārama me ngā Painga Matua
Mā te tātari maha-wāhanga ka huaki ake he whānuitanga o ngā āheinga whakamārama atu i ngā raraunga PP anake:
1. Te Whakatau Tatau Vp/Vs me te Tohu Wai-Lithology
Ko te ōwehenga Vp/Vs he tawhā tātaritanga e aro ana ki te āhua o te kohatu me te nui o te wai. I te nuinga o te wā, ka taea e te hau te whakaiti nui ake i te Vp i te Vs, nō reira ka heke te Vp/Vs i roto i ngā rohe hau (ahakoa me āta whakamārama me te horopaki). Mā te whakakotahi i ngā mōhiohio PP me PS, ka taea e ngā kaiwhakamāori te hanga mahere Vp/Vs hei āwhina i te wehewehe i waenga i ngā rohe onepū-paru, i ngā rohe kōhatu kī tonu i te hau, i ngā rohe wai rānei.
2. Te Whakaahuatanga o te Kapiti me te Taumahatanga
Mā te wehenga ngaru kutikuti me ngā rerekētanga azimuthal i roto i te urupare PS ka tohu i te aronga pakaru me te ahunga o te ahotea whakapae mōrahi. He mea whai hua tēnei mō te whakamahere puna whakapae, te whakaoho waipēhi, te whakatauira rānei i te hua o ngā puna pakaru.
3. Whakaahua i raro i te Rohe Hau, i te Rohe Pātara rānei
I ētahi wāhi, ka whakaitihia ngā whakaahua PP e te whakaitiiti, te marara rānei (hei tauira, i raro i ngā rohe hau pāpaku, i te basalt rānei). I ētahi wā, ka whakaratohia e te tahuritanga ngaru PS he whakaahua rerekē nā tōna rerekētanga o te aro. Ahakoa he wero anō hoki a PS (he iti ake te auau, he nui ake te haruru), i raro i ētahi āhuatanga ka taea e ia te whakaatu i ngā hanganga ngaro i roto i te PP.
4. Ngā Huanga Maha-Wāhanga me te Hurihanga
Mā te whakakotahitanga o ngā āhuatanga PP me PS ka taea te hurihanga rapa whai kōrero ake: ehara i te mea ko te aukati oro (AI) o te ngaru-P anake, engari ko te aukati kutikuti (SI) me ētahi atu tawhā rapa pērā i te ōwehenga Poisson, Lambda-Rho me Mu-Rho rānei (i raro i ētahi whakaaro). Ka whakapakari ake tēnei i te tātaritanga ahupūngao toka me te matapae mata.
Ngā Herenga me ngā Wero Whaihua
Ahakoa ōna painga maha, he maha ngā ngoikoretanga o te ru whenua maha-wāhanga:
– Ngā utu me te uauatanga teitei ake (ngā taputapu 3C, OBN/OBS, ngā whakaritenga QC tino kaha ake).
– He iti iho te kounga raraunga S/PS i te PP nā te haruru, te hononga, me te whaiti o te whānui raraunga.
– Te tukatuka uaua ake: te S pūmau, te anisotropy, me te hiahia mō ngā tauira Vp me Vs ōrite.
– Me whakauru atu ki ngā raraunga puna, te ahupūngao toka, me te matawhenua hei karo i ngā otinga kore-ahurei hei whakamārama.
Nō reira, ko ngā uara maha-wāhanga te mea tino pai ina whakamaheretia mai i te tīmatanga: he mārama ngā whāinga matawhenua (hei tauira, te mahere pakaru, te matapae Vp/Vs), e tautoko ana te hoahoa hopu i te azimuth, ā, kua whakaarohia kētia e te kaupapa tukatuka ngā hiahia whakamaori.
Te Katinga
Ko te tātaritanga maha-wāhanga i roto i te ru whenua tūhura he huarahi e whakawhānui ana i te matapihi tirotiro o raro i te mata mā te whakamahi i ngā mōhiohio mai i ngā momo ngaru neke atu i te kotahi me te ahunga nekehanga matūriki. Mā te whakakotahi i ngā raraunga PP me PS, me te whakamahi i ngā āhuatanga tairongo o ngā ngaru-S ki te anga toka, te anisotropy, me ngā pakaru, ka taea e te tātaritanga maha-wāhanga te whakapai ake i te māramatanga ki te lithology, ngā wai, me ngā āhuatanga ahotea. Ahakoa e hiahiatia ana he kohikohinga me te tukatuka uaua ake, he mea nui tōna uara tāpiri mō ngā whāinga wero me ngā hiahia tautuhi puna wai matatau. I roto i te horopaki o te tūhuratanga hou, e hiahia ana ki te whai huatanga me te tika o te whakatau, e kiia ana te ru whenua maha-wāhanga he taputapu matua mō te whakaiti i te koretake me te whakapai ake i te kounga o te whakamaoritanga o raro i te mata.
