Figure 16. Bottom-mounted Sea Data™ 635-12 directional wave gage mounted in tripod 

 using railroad wheels as corner weights 



Seismic wave gage 



Wave estimates based on microseismic measurements are an alternative 

 means to obtain wave data in high-energy environments. Microseisms are very 

 small ground motions that can be detected by seismographs within a few 

 kilometres of the coast. It is generally accepted that microseisms are caused 

 by ocean waves and that the amplitudes and periods of the motions correspond 

 to the regional wave climate. Comparisons of seismic wave gages in Oregon 

 with in situ gages have been favorable (Howell and Rhee 1990; Thompson, 

 Howell, and Smith 1985). The seismic system has inherent limitations, but 

 deficiencies in wave period estimates can probably be solved with more 

 sophisticated processing. Use of a seismometer for wave purposes is a long- 

 term commitment, requiring time to calibrate and compare the data. The 

 advantage of a seismograph is that it can be placed on land in a protected 

 building. 



34 



Chapter 3 Field Data Collection and Observation 



