ORIGINAL ARTICLE Another look at the 2009 seismic activity, Harrat Lunayyir, Saudi Arabia Ali K. Abdelfattah & Salvatore de Lorenzo & S. Almadani & M. Fnais & H. Alfaifi & N. Al-Arifi Received: 1 March 2018 /Accepted: 10 May 2019 # Springer Nature B.V. 2019 Abstract This study aims to recognize the influence of source- and path-effects on seismic spectra using the waveform data from the 2009 seismic activity, Harrat Lunayyir (HL), eastern flank of the Red Sea coastline, Saudi Arabia. This seismic activity is considered as a series of continuously evolving events reaching at some stage the maximum on 19 May 2009, with the largest shock of Mw 5.4, and then decayed. A total number of 218 events of magnitudes M L ≥ 2.0 were analyzed, which include the largest shock, 101 and 116 seismic events representing the seismic events within the early and decay stages, respectively. The data analysis using Frequency-time analysis revealed diversity patterns of frequency contents along the recorded seismic stations. Moreover, the modified WADATI diagram showed V P / V S variations of 1.7 ± 0.003 and 1.72 ± 0.002 before and after the occurrence of the largest-sized event among the HL seismic activity, respectively. Using the grid-search method to recover the space parameters representing the average source spectrum of each earthquake over the recorded seismic stations, estimates of source sizes and stress drops imply variations in self-similarity scaling relationship among the HL seismic activity. According to the results obtained from the current analyses, we propose a scenario began with an emplacement of seis- mic activity due to the local stress accumulation imports from an upward dike injection that is blocked by cooled and hardened magmatic materials in the upper crust from the earlier intrusions. The stress accumulation continued and was then released, at some stage, by the event having the maximum magnitude followed by seismic activities released due to stress relaxations. Keywords Spectralcharacteristics . V P /V S ratio . Source parameters . Tectonic and sequence activity . Saudi Arabia 1 Introduction The Arabian shield that lies to the east of the Red Sea rift is characterized by a wide distribution of ancient Ceno- zoic basaltic fields where local seismic activities oc- curred. Owing to this geodynamic process, many earth- quakes recently occurred in the shield. These earth- quakes include the 2009 Harrat Lunayyir (HL) earth- quake of Mw 4.8 (Abdelfattah et al. 2014) and the 2009 Badr earthquake of Mw 3.7 (Aldamegh et al. 2010), in the northwestern part of the shield. These earthquakes revealed the presence of normal faulting in the NNW- SSE striking plane. Recently, the 2014 Jizan earthquake of Mw 4.4 along the eastern Red Sea coastline, near the Yemen-KSA border, occurred. The focal mechanism solution shows dextral strike-slip faulting along the ENE-WSW striking plane (Abdelfattah et al. 2017). J Seismol https://doi.org/10.1007/s10950-019-09835-0 A. K. Abdelfattah (*) : S. Almadani : M. Fnais : H. Alfaifi : N. Al-Arifi Department of Geology & Geophysics, King Saud University, Riyadh 11451, Kingdom of Saudi Arabia e-mail: ali_kamel100@yahoo.co.uk S. de Lorenzo Dipartimento di Scienze della Terra, University di Bari BAldo Moro^, Via Orabona 4, I-70125 Bari, Italy