The concept of repeated earthquakes, often referred to as earthquake recurrence or seismic recurrence, relates to the idea that earthquakes can occur repeatedly in the same area or along the same fault. It is a fundamental concept in seismology and earthquake science. Here are the key points related to repeated earthquakes:

It's important to note that while scientists can estimate earthquake recurrence intervals based on historical and geological data, predicting the exact timing of future earthquakes remains challenging. However, by studying the concept of repeated earthquakes and their patterns, we can better prepare for seismic events and reduce their potential impact on society and infrastructure.

But To perform an Iterative Design and Analysis (IDA) study, you need to break down a time history record into several step on base of the most intensity of it ( for example 0.1 PGA, 0.2 PGA, 0.3 PGA, ......,10 PGA ) . For each of them, you apply the input motion to your structural model and analyze its response. every scale has a most response, you should write them in a curve on base the specific response( for example= drift) . The results are typically plotted on a curve (Sa-drift).

Therefore, the two concept which you mentioned are completely different.

The first concept is about several time history with several algorithm and different properties but the second one is about one specific time history.

Repeated earthquakes refer to a series of seismic events that occur in the same general region or along the same fault line over a period of time. These earthquakes are characterized by their recurrence in a specific geographical area and are often associated with tectonic plate boundaries.

The term "repeated earthquakes" implies that seismic activity is not a one-time occurrence but is rather a phenomenon that repeats itself due to ongoing tectonic processes. Tectonic plates are constantly moving, and their interactions can lead to the release of energy in the form of earthquakes.

Earthquakes can occur along faults, which are fractures in the Earth's crust where blocks of rock have moved past each other. As stress builds up along these faults, it is eventually released in the form of an earthquake. In regions with active tectonic activity, it is not uncommon to observe a series of earthquakes over time, with some areas experiencing repeated seismic events.

Monitoring and studying repeated earthquakes are essential for understanding the seismic behavior of a region, assessing earthquake hazards, and implementing effective earthquake preparedness and mitigation strategies. Scientists use seismological data to analyze the patterns and characteristics of repeated earthquakes, providing valuable information for earthquake prediction and risk assessment.