GADA MAI RURI TA YI WA GAƁAR KOGI HOTON CIKI LOKACIN AMBALIYA

Koguna da hanyoyi sukan raba hanya ɗaya. A ƙarƙashin gadoji, harsashai masu zurfi suna kaiwa mitoci da dama cikin laushin ƙasar kogi, inda ruwa ke kai da komowa tsakanin kogin da ruwan ƙarƙashin ƙasa. A lokacin manyan ambaliya, haɗari biyu suna haɗuwa: igiyar ruwa na iya zaizaye ƙasa daga harsashan, kuma ƙaruwar matsin ruwa a cikin ƙasa tana raunana gaɓoɓin kogin. Duk da haka sa ido har yanzu yana dogara ne kan ’yan na’urori a wurare kaɗan, rijiyoyi keɓaɓɓu da binciken hannu na lokaci-lokaci.

Giɓin hayaniya a gefen manyan hanyoyi

Masana girgizar ƙasa za su iya ɗaukar hoton ƙasa da raƙuman saman ƙasa (surface waves), har ma su bi ƙananan sauye-sauye a saurinsu a tsawon lokaci. Amma don su leƙa mitoci da dama ƙasa, suna buƙatar raƙuman ruwa masu ƙarancin mita (low-frequency). A gefen manyan hanyoyi, takardar ta lura, akwai giɓi: girgizar da teku ke haifarwa tana ƙasa da hertz 1 kuma tana leƙawa zurfi da yawa, yayin da motocin da ke wucewa galibi suna girgiza ƙasa sama da hertz 6 kuma suna leƙawa ba zurfi ba. Ababen hawa masu tafiya kuma ba su da kyau a matsayin tushe don maimaita auna, saboda ba sa taɓa zuwa daga wuri ɗaya sau biyu.

Distributed acoustic sensing (jin sauti da aka rarraba) tana warware matsalar na’urorin. Idan aka haɗa ta da wani na’ura mai suna interrogator, wata wayar fiber ta sadarwa da ke akwai tana zama dubban na’urorin girgizar ƙasa da tazarar mitoci kaɗan tsakaninsu. Abin da ya rage shi ne tushe mai kyau, mai dorewa.

Gadar a matsayin lasifika

Haipeng Li da abokan aikinsa a Jami’ar Stanford, tare da wani abokin aiki a Jami’ar Fasaha ta Nanyang a Singapore, sun yi amfani da wata wayar fiber ta sadarwa da ba a amfani da ita (“dark” fiber) a gefen Babbar Hanyar Gyeongbu ta Koriya ta Kudu, kusa da Cheongju. A kan gadar siminti mai tsawon mita 430 bisa Kogin Miho, an manne wayar a wajen saman gadar; a ɓangarorin biyu, tana tafiya ƙarƙashin ƙasa a gefen tudun hanyoyin shiga gadar. Sun naɗi bayanai daga 15 zuwa 25 ga Yulin 2025.

Kowace mota da babbar mota tana bugun saman gadar, wanda ke yin ƙara a mitocinsa na kansa. A kan gadar, fiber ɗin yana ɗaukar jerin sautuka a hertz 2.6, 2.8, 3.1, 3.4, 3.9, 4.3 da 4.6 — decibel 20.5 sama da hayaniyar gefen hanya. Ginshiƙai da gefunan gadar suna tura waɗannan girgizar cikin ƙasa, inda suke tafiya a matsayin raƙuman saman ƙasa a ƙetaren gaɓoɓin kogin biyu na fiye da mita 400.

Gadar tana aiki a matsayin matatar inji: bugun ƙafafun mota ba tare da tsari ba yana shiga, ruri mai dorewa yana fitowa. Saboda mota tana ƙetarewa kusan kowace daƙiƙa, da sauri fiye da yadda girgizar ke mutuwa, rurin ba ya tsayawa. Ababen hawa suna canza ƙarfinsa da decibel 2.7 tsakanin rana da dare, amma da ƙyar suna canza mitarsa, kuma ko a ƙololuwar ambaliyar saman gadar ya rasa decibel 1.2 kawai na ƙarfi.

Minti biyar don hoto mai tsabta

Ta amfani da wata fasaha mai suna seismic interferometry, tawagar ta mayar da bayanan da aka naɗa “harbe-harben kama-da-wane” (virtual shots), kamar an harba tushe a wuraren da aka zaɓa. Da gadar a matsayin tushe, raƙuman ruwa kai tsaye sun daidaita bayan tari ɗaya na minti 5, kuma sakamakon kowace sa’a ya kasance kusan iri ɗaya a duk tsawon ambaliyar.

Daga waɗannan raƙuman ruwa sun gina bayanan ƙasa a gaɓoɓin biyu:

• laushin ƙasar da ambaliya ta ajiye a mita 10 na sama, da saurin raƙuman shear tsakanin mita 250 zuwa 350 a daƙiƙa;
• ƙasar kogi mai ƙarfi har zuwa kusan mita 900 zuwa 1,000 a daƙiƙa;
• tsalle mai kaifi a kusan zurfin mita 56, wanda aka fassara a matsayin sauyawa zuwa abu mai ƙarfi da ke ƙarƙashin ƙasar kogi;
• gaɓar arewa ta ɗan fi ta kudu ƙarfi.

Kallon ambaliya tana jiƙa ƙasa

Naɗar ta kama wata damina da ba a taɓa gani ba. Ruwan sama mai ƙarfi ya sauka daga yammacin 16 ga Yuli zuwa safiyar 19 ga Yuli, ya kai ƙololuwa da milimita 51 a sa’a guda da sassafe a ranar 17 ga Yuli, kuma kogin ya ci gaba da hauhawa har zuwa 21 ga Yuli.

Hagu: ruwan sama da tsayin ruwan kogi. Tsakiya: sauyin saurin girgizar ƙasa a tsawon hanyar (shuɗi = a hankali), da saman gadar da launin toka. Dama: matsakaicin sauyi, yana raguwa bayan guguwar. — Figure 8, Li et al. (2026), arXiv:2610.09289.

Saurin girgizar ƙasa a gaɓoɓin kogin ya ragu yayin da guguwar ta iso, ya kasance ƙasa a lokacin ruwan saman, ya ɗan farfaɗo a lokacin da ababen hawa suka ragu a ƙarshen mako, sannan ya nutse zuwa mafi ƙasƙanci a lokacin da kogin ke janyewa — har kashi 1.0% a hankali fiye da kafin guguwar. A kan wasu na’urori biyu, saurin raƙuman ruwa a hertz 4.6, waɗanda ke jin kusan mita 50 ƙasa, ya faɗi daga mita 730 zuwa 678 a daƙiƙa. Masu binciken sun fassara hakan a matsayin laushin ƙasar da ta cika da ruwa: ruwa yana rage riƙon da ke tsakanin ƙwayoyin ƙasa kuma yana ƙara nauyi. Wani ɓangare mai jinkiri na martanin yana jinkiri da kwanaki da dama, watakila yayin da ruwan sama ke jiƙawa ƙasa a cikin ƙasa, ko da yake bayanan ba za su iya tantance matakin ruwan ƙarƙashin ƙasa ba.

Waya da ke nan tun tuni

Hanyar tana da iyakoki da masu binciken suka bayyana. Ba ta da ƙarfin ji sosai a mitoci kaɗan na sama, ta dogara ne kan ababen hawa, waɗanda zagayensu na yau da kullum da na mako suke barin alama a kan aunawar, kuma tana kaiwa kusan mita 450 ne kawai fiye da gadar. Amma fiber ɗin yana naɗar gadar kanta a lokaci guda, wanda ke taimakawa a raba sauye-sauyen tushen da sauye-sauyen ƙasa. Ana iya faɗaɗa hanyar zuwa gadojin jirgin ƙasa, madatsun ruwa ko injinan iska, kuma wata rana za ta iya taimakawa wajen sa ido kan zaizayewa a kewayen harsashan gadoji — ta amfani da wayoyin da tuni an binne su a gefen hanya.