AN N ALS OF GEOPH YSICS, 60, FAST TRACK 7, 2017; DOI: 10.4401/ A G-7541 1 Geoethics in Hollyw ood: How Can We Put More Reality into Fault Hazard Zoning? ELDON M. GATH TAN IA GON ZÁLEZ Earth Con su ltan ts In ter n ation al, San ta An a, CA, USA gath @earth con su ltan ts.com ; tgonzalez@earthconsultants.com Abstract The 15-km-long Hollywood fault extends through some of the most densely developed and expensive areas in southern Califor- nia. Given that billions of dollars of real estate could be impacted by an earthquake occurring on the fault, and that tens of thou- sands of people live near it, the seismic hazard posed by the Hollywood fault is concerning. But how much so? The City of W est Hollywood has required geological fault investigations and building avoidance of at least 15 meters from the fault’s active t race since the mid-1990s, resulting in numerous site investigations. Geologic studies in support of the Los A ngeles M etro subway and subsequent research found as-yet-unconfirmed equivocal evidence of an early Holocene-age (~8 ka) displacement event, and estimated strain rates of 0.3-0.9 mm/yr. In 2014, and following a “not-in-my-backyard” press campaign against the Hol- lywood M illennium project, the California Geological Survey zoned the eastern Hollywood fault as Holocene-active under their fault zoning program, requiring geological investigations and building setbacks from Holocene-age faults. In the years since the fault was zoned by the City of W est Hollywood and the California Geological Survey, millions of dollars have been invested in geological studies of the fault for building projects. A ll of these dollars have been reluctantly spent by the private sector, and all of this work has been eagerly done by consulting firms. The results? W ith only four exceptions, two in W est Hollywood, and two in the City of Los A ngeles, and all having opportunities for alternative interpretations, no Holocene-age fault displace- ments have been found. Instead, other studies have found definitive evidence that the fault has not ruptured in 10s to 100s of thousands of years. So what is the ethical alternative? Should we ignore the hazard posed by the fault? A re we geo-professionals too enamored of the financial gains such regulatory zoning provides that we are unwilling to suggest changes? Could we move past the “one size fits all” zoning that requires that single-family homes are held to the same standard as 40-story buildings? In the following sections we present several case studies along the Hollywood fault and provide our suggestions for a more pro- gressive program of fault hazard management. 1. IN TROD UCTION h e H ollyw ood fau lt is m ap p ed as an east- to n orth east-tren d in g stru ctu re alon g th e sou th ern m argin of th e San ta Mon ica Mou n tain s (locally referred to as th e H ollyw ood H ills), p lacin g late Ju rassic m et a- m orp h ic an d Cretaceou s to Miocen e gran itic an d sed im en tary rocks on th e n orth again st th e Qu atern ary-aged valley fill of th e H ollyw ood Basin . Most recen t m ap s gen erally sh ow th e H ollyw ood fau lt exten d in g from th e w est ban k of th e Los An geles River w estw ard , th rou gh th e cities of Los An geles, West H ollyw oo d an d Beverly H ills, a d istan ce of abou t 15 km (Fig. 1 an d 2). Th e fau lt is con sid ered p art of th e a p - p roxim ately 230-km -lon g fau lt system at th e sou th ern ed ge of th e Tran sv erse Ran ges p h ys i- ograp h ic p rovin ce of sou th ern Californ ia. N earby fau lts th at are also p art of th is system in clu d e th e Raym on d an d Sierra Mad re fau lts to th e east, an d th e San ta Mon ica, an d Malibu Coast fau lts to th e w est . 2. MAPPIN G OF THE HOLLYWOOD FAULT THROUGH TIME As early as 1931, H oots an d Kew p rep ared th e first com p reh en sive geologic m ap of th e area, an d in ferred th e San ta Mon ica –H ollyw ood T AN N ALS OF GEOPH YSICS, 60, FAST TRACK 7, 2017; DOI: 10.4401/ A G-7541 2 fau lts as bu ried stru ctu res at or n ear th e sh arp break in slop e alon g th e sou th ern m argin of th e San ta Mon ica Mou n tain s. Th e fau lt, or se ction s of th e fau lt zon e, w ere also m ap p ed by Lam ar (1970), H ill et al. (1978, 1979), Weber et al. (1980), Crook an d Proctor (1992), w ith m ap com p ilation s by Dibblee (1991a, b) an d Yerkes an d Cam p bell (2005). Th e m ost d etailed m ap p in g of th e H ollyw ood - San ta Mon ica fau lt w as d on e by Dolan et al. Figure 1: Location of the Hollywood fault at the base of the Hollywood Hills, forming the northern boundary to the Hol- lywood basin. The fault is considered a short segment of the approximately E-W to N E-W SW system of faults that in- clude the Santa M onica, M alibu Coast, Raymond and Sierra M adre faults shown on this figure. A dditional faults that are thought to be part of this system occur farther west and east, respectively, of the mapped image. Y ellow square shows the area covered in Figures 2 and 3. Figure 2: V arious interpretations of the location of the Hollywood fault using Dibblee’s (1991a, b) geologic maps as a base. N ote that in the east-central portion of the map, most researchers place the fault in almost the same area, whereas to the west and east, the interpreted fault locations vary, sometimes significantly. AN N ALS OF GEOPH YSICS, 60, FAST TRACK 7, 2017; DOI: 10.4401/ A G-7541 3 (1992, 1997), w h o u tilized U.S. Geological Su r- vey 1920s vin tage 5-foot (~1.5 m ) con tou r top o- grap h ic m ap s of th e area to m ap scarp s, fan s an d oth er p oten tially fau lt -related top ograp h ic featu res n ow h id d en by u rban d evelo p m en t. Dolan et al. (1992, 1997) id en tified several lin e- ar scarp s an d faceted sou th -facin g rid ges (see yellow zon es in Fig . 2) th at th ey in terp reted as th e n ear-su rface exp ression of th e fau lt. Wh ere th e scarp s are broad featu res 15 to 60+ m w id e, th e research ers com bin ed th e geom orp h ic d ata w ith su bsu rface in form ation obtain ed from g e- otech n ical an d grou n d w ater stu d ies in an a t- tem p t to better con strain th e location of th e m a- jor traces of th e H ollyw ood fau lt. H oots (1931) an d oth er early research ers h ad in ferred th e fau lt to be p rim arily a n orth -d ip p in g reverse stru ctu re resp on sible for th e grow th of th e a d - jacen t H ollyw ood H ills. H ow ever, based on th e fau lt’s lin ear trace an d steep 80- to 90-d egree d ip s observed in d ow n -h ole logged borin gs, Dolan et al. (1997, 2000) in te rp reted th e fau lt as p rim arily left-lateral strike-slip w ith a sm all am ou n t of n orth -sid e u p , r everse com p on en t. N otably, in th e West H ollyw ood an d Beverly H ills areas, Dolan et al. (1997, 2000) in terp reted th e H ollyw ood fau lt sou th of th e m ain break in slop e th at H oots an d Kew (1931) an d m ost oth - er research ers h ad u sed to in fer th e location of th e fau lt. Several fau lt-location stu d ies in th e West H ollyw ood area h ave been con d u cted sin ce th e m id -1990s. Abou t a th ird of th ese stu d ies h ave en cou n tered or in terp reted fau lts, an d th e location s of th ese h ave rou gh ly agreed w ith Dolan et al.’s (1997, 2000) fau lt scarp s, alt- h ou gh th e zon e of fau ltin g h as been sh ow n to be w id er an d m ore com p lex, in terp reted to con sist of both n orth -d ip p in g reverse- sep aration stru ctu res, an d sou th -d ip p in g n or- m al fau lts w ith in th e h an gin g w all. Sign ifican t- ly, h ow ever, on ly on e of th ese fau lts h as been in terp reted as H olocen e a ctive, based on th e fin d in gs at th e Su n set Millen n iu m an d H ou se of Blu es sites (on th e far left in Fig. 3), w h ere rad iocarbon -d ated sam p les w ere collected from above an d below th e fau lt zon e in d ow n -h ole logged borin gs. Several of th ese stu d ies also fou n d th at th e steep step in th e bed rock th at Figure 3: Part of the zone of required investigation (yellow area) established by the California Geological Survey (CGS, 2014) for the Hollywood fault. A ny property within the yellow zone is required to be investigated for possible active faulting prior to it being developed or re-developed. Blue stars denote sites discussed in the text where faults found to be not active were exposed in trenches or were interpreted from transects of CPTs and borings; red stars show the only sites where radiocarbon-dated sediments have suggested the occurrence of Holocene-active faults. The black lines show the location and extent of transects across the fault zone that were conducted between the 1980s and approximately 2014. Since the fault was zoned, several additional studies have been conducted; only a few of these (such as Cherokee, Hudson, and Hollywood M illennium) are included here. AN N ALS OF GEOPH YSICS, 60, FAST TRACK 7, 2017; DOI: 10.4401/ A G-7541 4 w as p reviou sly in terp reted as a fau lt scarp (H oots an d Kew , 1931; Dibblee, 1991a, b) is an an cien t beach seacliff. Tren ch es an d borin gs h ave exp osed an old m arin e abr asion (w ave- cu t) p latform an d associated m arin e d ep osits estim ated to be at a m in im u m 400,000 to 900,000 years old (su m m arized in H ern a n d ez an d Treim an , 2014; H ern an d ez, 2014). Sim ilar m arin e sed im en ts h ave been observed at d ep th both to th e w est an d east, in Beverly H ills an d H ollyw ood , resp ectively. Th e H ollyw ood fau lt w as in terp reted or o b- served in som e of th e tran sects con d u cted for in frastru ctu re p rojects su ch as th e Los An geles (LA) Metro Red Lin e alon g Cam in o Palm ero – Martel Aven u e, an d La Brea Aven u e, th e LA MetroRail p roject alon g Cah u en ga Bou levard , an d storm d rain tren ch es alon g Vista Street an d Fu ller Aven u e (Dolan et al., 1997). Dolan et al. (2000) revisited th e Cam in o Palm ero -Martel Aven u e location an d u sed a series of closely sp aced d ow n -h ole logged borin gs to better lo- cate an d stu d y th e fau lt. Th e fin d in gs from th at stu d y su ggested th at th e m ost recen t su rface - ru p tu rin g earth qu ake (MRE) on th e H ollyw ood fau lt occu rred abou t 7,000 to 9,500 years ago, w ith a p ossible p en u ltim ate even t abou t 22,000 years ago, in d icatin g a lon g in terval betw een earth qu akes, an d an u n con firm ed estim ated strain rate of 0.3-0.9 m m / yr. Given its len gth , th e H ollyw ood fau lt is on ly cap able of gen era t- in g abou t a Mw ~ 6.6 earth qu ake. To p rod u ce a larger-m agn itu d e earth qu ake requ ires th at th e fau lt ru p tu re togeth er w ith oth er fau lts to th e w est an d east, su ch as th e San ta Mon ica, Mali- bu Coast an d Raym on d fau lts. Th e existin g p aleoseism ic d ata, h ow ever, sh ow th at each of th ese fau lts h as a sign ifican tly d ifferen t eart h - qu ake h istory, w ith th ou san d s of years b e- tw een even ts on d ifferen t fau lts. Th u s, th e available d ata su ggest th at th e H ollyw ood fau lt ru p tu res in d ep en d en tly, h as a slow rate of slip , an d takes th ou san d s of years to reach its brea k- in g p oin t. Assu m in g th e MRE age an d strain rate are correct, th e fau lt h as accu m u lated b e- tw een 2.1 an d 8.5 m of strain , u n likely h igh valu es for su ch a sh ort fau lt. Follow in g th e City of West H ollyw ood exa m - p le from th e m id -1990s, th e City of Los An geles began requ irin g fau lt stu d ies in th e H ollyw ood area in th e early 2000s. Th en in 2014, th at p o r- tion of th e H ollyw ood fau lt in th e H ollyw ood qu ad ran gle w as zon ed by th e Californ ia Ge o- logical Su rvey u n d er th e p rovision s of th e 1972 Alqu ist-Priolo Earth qu ake Fau lt Zon in g Act (Figu re 3; H ern an d ez an d Treim an , 2014; H e r- n an d ez, 2014; CGS, 2014). As a resu lt of th ese requ irem en ts, several stu d ies h ave been co n - d u cted in th e H ollyw ood area (su m m arized in H ern an d ez an d Treim an , 2014; H ern a n d ez, Figure 4a: M ap showing the extensive data set used to evaluate the Hollywood M illennium sites, including trenches (in light turquoise), CPTs (in red), and continuously sampled borings (in blue). The inferred location of the Y ucca Street section of the Hollywood fault shown by the black dots. Two faults (orange lines) were interpreted from the sub- surface data; these faults are minor and have not moved in at least 100,000 years. Figure 4b: Photograph showing a portion of the 9+ m deep trench excavated in the parking lot of the Tower Records building, which is also the East M illennium site. The footprint of the trenches is shown in light turquoise on the figure to the left. A demonstrably not active fault with about 50 cm of total displacement was exposed near the bottom of the trench. Photo courtesy of Group Delta Con- sultants. AN N ALS OF GEOPH YSICS, 60, FAST TRACK 7, 2017; DOI: 10.4401/ A G-7541 5 2014). Both th e n orth ern an d sou th ern traces sh ow n on th e eastern on e-th ird of th e zon in g m ap h ave been th e su bject of th ese stu d ies. H ow ever, on ly tw o of th ese con su ltin g stu d ies, both on H igh lan d Aven u e, h ave in terp reted active (H olocen e) traces of th e H ollyw ood fau lt w ith in th e zon e. 3. SITE-SPECIFIC FAULT STUD IES 3.1 Hollyw ood Millennium Sites and Hudson Avenue Th e p rop osed East an d West H ollyw ood Mil- len n iu m sites (far righ t on Figu re 3) exten d across th e Yu cca Street section of th e H olly- w ood fau lt as m ap p ed by CGS on th eir Alqu ist-Priolo (A-P) m ap . Th e geotech n ical con su ltan ts for th is p roject (Grou p Delta Co n - su ltan ts) p u sh ed m ore th an 100 con e p en e- trom eter test (CPT) p robes, d rilled an d logged m ore th an 30 con tin u ou sly cored borin gs, an d excavated an d logged tw o tren ch es w ith a com bin ed total len gth of m ore th an 120 m (Fig . 4). Th ese stu d ies h ave sh ow n th at th e area is u n d erlain by ~10 m of H olocen e-aged allu viu m d ep osited w ith in a can yon th at w as carved in to Pleistocen e-aged m u d flow d ep osits an d , in th e n orth ern p ortion of th e stu d y area, Top an ga Form ation (~ 15Ma) bed rock an d old er allu vial fan d ep osits th at sign ifican tly p re-d ate th e m u d flow d ep osits. Th ese su bsu rface stu d ies su ggest th e p resen ce of at least tw o m in or fau lts u n d er th e area, w ith last m ovem en t on th ese fau lts occu rrin g betw een abou t 100,000 an d 150,000 years ago. Th u s, th e area is n ot u n d erlain by active fau lts, con trary to th e CGS’ m ap th at in d icates th e active H ollyw ood fau lt exten d s th rou gh th is site. Sim ilarly, CPTs an d borin gs d rilled alon g a section of H u d son Av e- n u e en cou n tered a d iscon tin u ity in th e d eep er layers th at is eith er an er osion al su rface or a fau lt. Th e featu re is overlain by several u n bro- ken layers of old er allu v iu m m od ified by soil- form in g p rocesses. Th e d egree of soil d evel- op m en t exh ibited by th ese allu vial sed im en ts in d icate th at if th e d iscon tin u ity is fau lt- con trolled , th e fau lt h as n ot m oved in at least 50,000 years. Th is estim ate is con sid ered a m in - im u m valu e given th at m ost of th e overlyin g u n broken soils w ere tru n cated , in d icatin g sig- n ifican t erosion al p eriod s. 3.2 Cherokee Avenue Sites To d ate, th ree sep arate stu d ies h ave been co n - d u cted off Ch erokee Aven u e, in H ollyw ood . Th e first stu d y fou n d fau lted bed rock w ith n o overlyin g allu vial sed im en ts from w h ich to d e- term in e fau lt activity; th e CGS ch ose to con sid - er th e fau lt active (see H ern an d ez et al., 2014). In 2016 w e con d u cted a stu d y im m ed iately to th e sou th . Ou r eastern m ost tren ch es exp osed th e H ollyw ood fau lt p lacin g bed rock of th e Top an ga Form ation (Tt) ov er Pleistocen e age allu viu m (Fig. 5). Th e fau lt d ip p ed to th e n orth at abou t 40 d egrees at th e bottom of th e tren ch - es, bu t rolled over to n early h orizon tal, form in g th e con tact betw een tw o old er allu vial d ep o s- its. Th e fau lt tip th ru st Qoal2 u n d er Qoal3 d u r- in g its last su rface-ru p tu rin g earth qu ake. Th e fau lt cou ld n ot be traced u p w ard in to th e u p - p er section of th e Qoal2 u n it, as th is con tact w as in ten sely biotu rbated . In a p arallel tren ch , h ow ever, th e top of th e Qoal1 u n it w as clearly n ot broken , so w e are certain th at th e fau lt h as n ot m oved sin ce th e soil in th e Qoal1 u n it form ed . Ou r age estim ates for th at u n it, based on d egree of soil d evelop m en t, ran ge from abou t 160,000 to 230,000 years, so th is fau lt h as n ot m oved in at least 160,000 years, a fin d in g th at w as later con firm ed by oth ers on an ad ja- cen t p rop erty. 4. D ISCUSSION Desp ite exten sive an d costly in vestigation s, e v- id en ce th at th e H ollyw ood fau lt is active r e- Figure 5: Log of southern end of Trench ECI-1 at the Cherokee A venue site showing the fault in red, and the geologic units described in the text. AN N ALS OF GEOPH YSICS, 60, FAST TRACK 7, 2017; DOI: 10.4401/ A G-7541 6 m ain s elu sive. Th e p u blish ed fin d in gs of an early H olocen e d isp lacem en t, an d m ed ia cov- erage of op p osition to th e H ollyw ood Millen - n iu m p roject led th e CGS to con sid er th e fau lt su itable for A-P zon in g. Th e tw o zon in g criteria u sed by th e CGS are “su fficien tly active” (i.e. H olocen e/ 11,700 ybp ) an d “w ell d efin ed .” If th e few stu d ies su ggestin g H olocen e activity (H ern an d ez an d Treim an , 2014), are correct, th e H ollyw ood fau lt m igh t m eet th e extrem e m in im u m con d ition of H olocen e-active, bu t its active trace is certain ly n ot w ell d efin ed , as d em on strated by th e n u m erou s oth er stu d ies attem p tin g, an d failin g, to fin d it. Con sid erin g th e m illion s of d ollars in vested by p rivate d e- velop ers in th ese stu d ies, can w e n ot d evelop a m ore p rogressive m eth od of ach ievin g eart h - qu ake safety alon g th is, an d oth er sim ilarly p oorly d efin ed , low -slip fau lts? Californ ia law for active fau lt zon in g sp ecifies avoid an ce of th e fau lt trace as th e on ly p erm it- ted m itigation altern ative if th e fau lt h as exp e- rien ced even a sin gle, m in or H olocen e d is- p lacem en t. Th is bin ary, on e -size-fits-all ch oice h as led m an y ow n ers to n ot u p d ate th eir exist- in g old er bu ild in gs becau se a fau lt stu d y w ou ld be requ ired before th ey can red evelop . If a H olocen e fau lt is fou n d u n d er th eir site, th e ow n er w ou ld likely be p roh ibited from u n d e r- takin g stru ctu ral m od ern ization for seism ic safety. Th u s, on e of th e law ’s u n in ten d ed co n - sequ en ces is th e p reserv ation an d con tin u ed u se of stru ctu res th at are seism ically u n safe from h igh -p robability region al earth qu ake even ts becau se of th e low -p robability of su rface fau lt ru p tu re th rou gh th eir site. We p rop ose a m ore p rogressive ap p roach to m itigate th e h azard of su rface fau lt ru p tu re th at takes in to accou n t th e forty years of earth qu ake geology kn ow led ge gain ed sin ce th e law w as en acted . We su ggest th at su rface fau lt ru p tu re m itig a- tion be in corp orated in to th e bu ild in g cod e, r a- th er th an bein g cod ified in to law . In d oin g so, geologists w ill be tasked w ith d eterm in in g th e fau lt’s location an d ru p tu re kin em atics, tim in g of p rior even ts, an d estim ated tim e to th e n ext even t. Th en , based on th e typ e of stru ctu re p rop osed , a risk m an agem en t ap p roach w ou ld be em p loyed scaled to th e h azard an d th e risk, sim ilarly to all oth er geologic risk factors (seism ic sh akin g, grou n d failu re, slop e failu re, liqu efaction , flood in g, etc.) th at are alread y con sid ered in th e bu ild in g cod e. Th u s, for sin - gle-fam ily resid en tial h om es, a fau lt w ou ld be su bject to m itigation requ irem en ts if th e fau lt lies w ith in 500 years of its average recu rren ce in terval. For larger resid en tial an d com m ercial stru ctu res, th e fau lt w ou ld be su bject to m itiga- tion if it lies w ith in 1000 years of its average recu rren ce in terval, an d for critical in frastru c- tu re an d facilities, th at in terval cou ld be 1500 or 2500 years. Th ese h azard w in d ow s are sim ilar to th ose for seism ic stru ctu ral d esign , liqu efa c- tion an d lan d slid e geotech n ical stabilization , an d exceed th ose for flood h azard s. Mitigation altern atives m igh t in clu d e stru ctu ral isolation or rein forcem en t, soil stren gth en in g, or avoid - an ce, d ep en d in g u p on th e an ticip ated fau lt’s d isp lacem en t, site con d ition s, an d econ om ic or social valu e. Con tin u in g d ow n th e forty -year-old p ath of strict avoid an ce for an y H olocen e-age fau lt, d e- sp ite its d isp lacem en t h istory or m agn itu d e, can n o lon ger be d efen d ed as a cost -effective solu tion to im p rove p u blic safety. In telligen t an d p rogressive m itigation of kn ow n an d p rop erly qu an tified h azard s is th e basis of all p erform an ce-based d esign s, an d it is tim e for Californ ia’s geologists, an d th e Californ ia Ge o- logical Su rvey, to m ove on from th e A -P Act by eith er m od ern izin g or su n settin g it, an d lettin g th e bu ild in g cod e p rocess h an d le fau lt ru p tu re h azard as ju st an oth er geologic factor in lan d p lan n in g an d d evelop m en t. It is th e eth ical th in g to d o. ACKN OWLEDGEMEN TS Th an k you to Maria H erzberg of Earth Co n - su ltan ts In tern ation al for p rep arin g Figu res 1 th rou gh 3. Th e rep ort w as im p roved follow in g com m en ts an d ed its to th e origin al m an u scrip t p rovid ed by Um berto Fracassi, an an on ym ou s review er, an d Giu sep p e Di Cap u a. Th an k you for you r valu able an d h on est feed back . REFEREN CES California Geological Su rvey (CGS) (2014). 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