Waleed N. Al-Omar

ID# 240292

GEOPH 503 -HW#2-

Lithosphereic strength and its relationship to Te and Ts!

With the possibility of estimating Te and Ts at oceanic and continental lithosphere, ths paper shed some light on the relationship between the elastic thickness and the seismogenic thickness claiming that Te >>Ts in continental lithosphere, due to its different rheology, but not in the oceanic lithosphere, due it relatively simple structure. It shows that Te and Ts are different in the ways they contribute to strength of earth’s lithosphere

Questions:

1)      Why Seismic activity in the oceanic lithosphere is limited to a depth range of around 15km?

Ans: at such depth range a semi-brittle/semi ductile strain rate dependent plastic flow takes over. Frictional component doesn’t present an important factor at such depths. In short, at depth where ductile behavior is dominant earthquakes are rare, whether it is related to oceanic or continental lithosphere.

2)      Is there a difference in the mechanism that originates shallow and deep earthquakes?

Ans: in general shallow earthquakes are related to the absolute rock strength and deep seismic activity is not related to frictional sliding that follows Bayerlee’s law. Hence, deep earthquakes are weakly related to absolute rock strength.

3)      Could Te and Ts follow each other and Te is always less than Ts

Ans: From studies conducted recently, the above is possible with reexamining the data and trying to determine the, accurately, the depth associated with earthquakes epicenter and Moho depths. They found that Te and Ts follow each other in different regions. That entails the strength lies on the uppermost layers of the continental crust, but it doesn’t say much about the oceanic crust since it is bound by different factors.