Abstract
Microtremors have been utilized in the earthquake engineering field as an effective tool to investigate underground structures from the ground surface measurements indirectly. In this paper, studies on measurements of microtremors are reviewed focusing on the engineering utilizations. Reviewing is carried out classifying the microtremors into two kinds of short and long period.
Initially, short period microtremors are discussed. At the beginning of this century, the first measurement of short period microtremors was carried out, finding that microtremors reflect well ground vibrational characteristics during an earthquake. After that many studies continued to investigate the relation with the dynmamic characteristics of shallow underground structures. Among these studies Kanai and his colleagues' works are distinguished and along their results a standardized method for measurements and analyzing of microtremors is described here. Typical examples for practical applications are referred to including the Kanai's discrimination method for types of ground.
Secondly, studies of long period microtremors are discussed which have been developed during the past 20 years in order to investigate deep underground structures up to several kilometers. These studies have been initiated and accelerated by the circumstances of the recent expansion of building height and width. Examples of the field measurements and their interpretation in earthquake engineering use are also introduced.
In conclusion an applicability of microtremors to earthquake engineering field is summarized and further problems to be solved are pointed out.
