Mystery tremors on Danish Baltic island puzzle scientists

A series of minor tremors recorded on the Danish Baltic island of Bornholm has puzzled scientists, who now say they were caused by “acoustic pressure waves from an unknown source”. At first the tremors on Saturday were thought to have been caused by earthquakes. Then, seismologists theorised they originated from controlled explosions in Poland, more than 90 miles (140km) to the south.

tips

minor：较小的；次要的；轻微的

tremor：震动；颤动（trem- =quiver 颤抖）

puzzle：难题；困惑；vt. 使困惑

acoustic：听觉的；声学的；音响的

seismologist：地震学家（seismo- =earthquake 地震，希腊语 seismos）

theorise：推理；建立理论