Fundamental Review of State Government Seismological Laboratory John Anderson, Director

Figure 1a. Earthquakes of Nevada with magnitude of 2.0 or larger. This figure was generated by an automated search of the Seismological Laboratory’s catalog via the world wide web. The web can be accessed at:

Figure 1b. Earthquakes of Nevada with magnitude of 3.0 or larger. This figure was generated by an automated search of the Seismological Laboratory’s catalog via the world wide web. The web can be accessed at:

Figure 1c. Earthquakes of Nevada with magnitudes of 5.0 or larger.

Figure 2. Time-magnitude plot of earthquakes in Nevada and adjacent regions. Only earthquakes with magnitude of 5.0 or greater are shown. The increased numbers of earthquakes at low magnitudes in recent years is the result of development of local seismic networks.

Figure 3. Fault map of Nevada, from dePolo (1998): A reconnaissance technique for estimating the slip rates of normal-slip faults in the Great Basin, and application to faults in Nevada, U.S.A. (Ph.D thesis, Univ. of Nevada, supervised by John Anderson)

Figure 4. Microwave network operated by the Seismological Laboratory to acquire seismic network data in Reno.

Figure 5. Comparing seismograms: In this figure we compare recordings of ground motion (called seismograms) from two kinds of instruments. Amplitude of the ground motion is on the vertical axis and time is on the horizontal axis. The typical, older style seismometer produces the oddlooking seismogram that looks like a black strip with a long tail. The modem seismometer that accurately records the ground motion shows the amplitude of ground shaking is much different with peaks and troughs that eventually diminish with time. The older instruments were designed for locating earthquakes based on the time that the first shaking occurs at a station. However, this is not sufficient if we are to understand the relationship between damage and the intensity of shaking based on the amplitude of the ground motion. Unfortunately the older instruments hit their stops (seismologists say the data is "clipped") at a very low intensity of shaking. Even a moderate earthquake "clips" all of the older instruments and thus they provide no useful information as to the severity of shaking. Modem instruments have the ability to record accurately both small and large motions to give a true picture of the amplitude of the waves and thus the intensity of shaking. The modern instruments automatically transmit this signal to a computer. Within minutes, the computer can process these digital signals from different instruments to generate maps of the ground shaking for emergency response. With enough modem instruments in an area, we can immediately compare levels of shaking in different areas to know which areas are likely to be affected the most. (Figure courtesy of Seismological Society of America)

Figure 6. Nevada seismic network in 1990.

Figure 7. Nevada seismic network in 2000.