  A new surface-rupture-length ($SRL$) relationship as a function of magnitude
($\mathbf{M}$), fault thickness, and fault dip angle is presented in this
paper. The objective of this study is to model the change in scaling between
unbounded and width-limited ruptures. This is achieved through the use of
seismological-theory-based relationships for the average displacement scaling
and the aid of dynamic fault rupture simulations to constrain the rupture width
scaling. The empirical dataset used in the development of this relationship is
composed of $123$ events ranging from $\mathbf{M}~5$ to $8.1$ and $SRL~1.1$ to
$432~km$. The dynamic rupture simulations dataset includes $554$ events ranging
from $\mathbf{M}~4.9$ to $8.2$ and $SRL~1$ to $655~km$. For the average
displacement ($\bar{D}$) scaling, three simple models and two composite models
were evaluated. The simple average displacement models were: a square root of
the rupture area ($\sqrt{A}$), a down-dip width ($W$), and a rupture length
($L$) proportional model. The two composite models followed a $\sqrt{A}$
scaling for unbounded ruptures and transitioned to $W$ and $L$ scaling for
width-limited events, respectively. The empirical data favors a $\bar{D} \sim
\sqrt{A}$ scaling for both unbounded and width-limited ruptures. The proposed
model exhibits better predictive performance compared to linear
$\log(SLR)\sim\mathbf{M}$ type models, especially in the large magnitude range,
which is dominated by width-limited events. A comparison with existing $SRL$
models shows consistent scaling at different magnitude ranges that is believed
to be the result of the different magnitude ranges in the empirical dataset of
the published relationships.
