The 1984 morgan hill, california, earthquake

Area of Science:

• Seismology
• Earthquake Science
• Geophysics

Background:

• The Calaveras fault zone, east of San Jose, California, experienced a significant seismic event.
• A magnitude 6 earthquake had previously occurred on this segment in 1911, suggesting potential for recurrence.
• Despite the historical context, no short-term seismic precursors were identified before the 1984 event.

Purpose of the Study:

• To analyze the rupture characteristics and ground motion of the 1984 Morgan Hill earthquake.
• To understand the factors contributing to the focused pattern of strong seismic radiation.
• To investigate the reasons for the lack of short-term earthquake prediction.

Main Methods:

• Analysis of seismic data from the 1984 Morgan Hill earthquake.
• Investigation of rupture propagation direction and seismic radiation sources.
• Examination of strong motion recordings, including peak ground acceleration.

Main Results:

• The earthquake involved a unilateral rupture propagating south-southeast along a 30-km fault segment.
• An energetic seismic radiation source near the southeast end significantly influenced ground motion.
• An exceptionally high horizontal acceleration of 1.29g was recorded at a dam abutment near the rupture's end.

Conclusions:

• The 1984 Morgan Hill earthquake's rupture dynamics led to a highly localized and intense strong motion pattern.
• The absence of predictable short-term precursors highlights challenges in earthquake forecasting for this fault segment.
• Understanding rupture complexity is crucial for seismic hazard assessment in the region.