She is sleeping here so she won't have to travel from Riverdale in the morning.
她晚上住在这儿,免得早上从Riverdale赶过来。
The second marks the arrival of transverse vibrations which travel more slowly and arrive several minutes after the first.
然后记录下的是横向波的到达,横向波比纵向波传播得慢,在纵向波到达几分钟后才能到达。