以摩擦試驗探討斷層滑移對於微生物生存的影響;The effect of seismic fault deformation on the survivability of microorganisms: an experimental approach

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题名:	以摩擦試驗探討斷層滑移對於微生物生存的影響;The effect of seismic fault deformation on the survivability of microorganisms: an experimental approach
作者:	孫東容;Sun, Dong-Rong
贡献者:	地球科學學系
关键词:	地質微生物;地震;斷層滑移;摩擦試驗;熱增壓;geomicrobiology;earthquake;fault propagation;rotary shear;thermal pressurization
日期:	2021-10-22
上传时间:	2021-12-07 11:51:08 (UTC+8)
出版者:	國立中央大學
摘要:	地底下的微生物佔全球生物質量的五分之一，並在生物地球化學循環中扮演非常重要的角色。另一方面，地震是地殼釋放應力的一個普遍現象，地震破裂在斷層帶中造成物質的粉碎並驅動不同的物理化學作用。目前為止，有關微生物與地震之間的研究，主要是於地震前後分析斷層周圍的水樣，探討微生物多樣性和群落結構的變化，間接獲得兩者的交互作用，卻從未有過地震破裂對微生物增殖的直接影響評估。藉由特殊設計的岩石變形容器，本研究分別對混有Shewanella oneidensis 和 Pseudomonas putida (兩種常見的細菌)的飽和水高嶺土樣本進行旋剪試驗，以研究微生物遭受地震破裂的生存潛力。含微生物的樣品在10百萬帕的正(軸)向應力下以地震速率(1公尺/秒)滑移3公尺(約規模7的地震)與10公尺(約規模7.5的地震)，並在實驗前後以直接計數法計算完整細胞的數目，以及連續稀釋法估算生存細胞的數目。結果顯示，壓密過程(旋剪前)對不同菌種有不同程度的破壞。比對旋剪前的數據，旋剪後的完整細胞大量減少(一個數量級以內)，存活細胞更是隨著滑移距離增加而呈對數的減少(可達三到五個數量級)。根據已發表之斷層行為與機制，我們推測地震破裂時: (1)初期的粉碎作用大量減少細胞的數量，而弱化機制熱增壓的驅動使黏土顆粒間的間隙變大，使完整細胞較易被保存(與存活);(2)菌株遭受規模7的地震仍可存活;(3)遭受規模7.5的地震，因為溫度超過這些菌株所能承受的最大值，導致菌株的滅絕。本研究論證在地震破裂後斷層帶的微生物的存活與滅絕，並且說明熱增壓作用為微生物存活的機制。;Subsurface microorganisms have been estimated to constitute 1/5 of the global biomass, quantitatively playing an important role in biogeochemical cycling. On the other hand, earthquake is a common phenomenon of stress release in the crust. Seismic ruptures cause comminution of materials in the fault zone and drive different physicochemical actions. To date, the studies related to the interaction between microorganisms and earthquake focused on the change of microbial diversity and community structure by analyzing water sample around faults before and after an earthquake. However, the effects of seismic ruptures on microbial proliferation have never been investigated. In this study, by using a purpose-built sample holder, we applied rotary shearing on the water-saturated kaolinite amended with two kind of bacterial strains, Shewanella oneidensis and Pseudomonas putida, which are commonly found in various environments, to investigate the potential of microbial survival after seismic ruptures. To simulate fault propagation, the water-saturated kaolinite was deformed at a seismic slip rate of 1 m/s for a total slip of 3 m (~M7 earthquake) or 10 m (~M7.5 earthquake) under a normal stress of 10 MPa. Results showed that compression damaged the cells in different levels to strains. Intact and viable cells decreased by tens of percent and orders of magnitude after shearing, respectively. Based on the fault behavior and mechanism in publication, we infered that when an earthquake ruptures: (1) The initial comminution greatly reduce the number of cells. And the following weakening mechanism driven by thermal pressurization enlarge the gaps between clay particles, making more intact cells to be preserved and survived. (2) The strains can survive an earthquake of magnitude 7. (3) With an earthquake of magnitude 7.5, temperature raised during shearing imposes great stress on these strains, leading to the extinction. This study demonstrates the survival and extinction of microorganisms in the fault zone after a seismic rupture, and suggests that thermal pressurization is the mechanism for the survival of microorganisms.
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