If they do not, previously unsuspected faulting could account for the misclosure.是什么意思？

If they do not, previously unsuspected faulting could account for the misclosure.

如果他们不这样, 尚未发现的断层可能就是造成不闭合的原因.

if

conj. 如果，倘若，即使，〈口〉是否，假设；n. 条件，设想；

例句
She was old enough to absent herself from the lunch table if she chose...
她长大了，可以自己做主不来吃午餐了。

they

pron. 他/她/它们，人们，大家，政府，当局，她们；

例句
The storms had abated by the time they rounded Cape Horn.
他们绕过合恩角时，暴风雨已经减弱。

do

aux. 构成疑问句和否定句，代替动词，用于加强语气；vt. 做，干，进行，从事；vi. 表现，进展，引起，行过；n. 社交聚会，社交活动，宴会；

例句
Rachel was going to do something about Jacob...
蕾切尔将对雅各布有所行动。

not

adv. 不，[用以表示否定、否认、拒绝、禁止等]不是，几乎不，未必，没有[用于否定后面的词或短语]；

例句
It became very clear that the incident was not just an aberration, it was not just a single incident.
事实已经很清楚，这件事不是偶发的，它并不是一起孤立的事件。

previously

adv. 事先，以前，仓促，“previous”的派生；

例句
Spassky had never previously lost to his antagonist.
斯帕斯基以往从未输给过他的对手。

faulting

n. 断层作用，故障；

例句
It appears to be a sharp anticline with a strong suggestion of faulting on one side.
它看来象是在一边有着明显的断层迹象的陡峭的背斜.

could

aux. “can”的过去式，能够，打算，用于假设语气的条件句，用于虚拟语气的结论句；

例句
The regulations were relaxed and the prisoners could get out and about a bit.
规定有所放宽，犯人可以出去短暂放风。

account

n. 账，账目，存款，描述，解释；v. 认为是，视为；

例句
I had two accounts with Natwest, a savings account and a current account.
我在国民威斯敏斯特银行有两个账户，一个储蓄账户和一个活期存款账户。

for

prep. 为，为了，倾向于，关于，当作；conj. 因为，由于；

例句
I've come looking for a bit of advice.
我特来讨教。

the

art. 指已提到的人（物），指说话人与听者已知的人（物），用于独一无二的事物前，与形容词最高级和序数词连用；

例句
He did have a real knowledge of the country...
他对该国的确知之甚多。